Glossary

This glossary is divided in two sections:

  • The first section contains Tezos generic terms (i.e., which are not related to a particular protocol), such as Tezos or block.

  • The second section contains terms defined by the economic protocol, such as Tez/XTZ, account, smart contract, or delegate. The list of terms in this section and/or their definitions may be different for other protocol versions.

Tezos terms

Block

The Tezos blockchain is a linked list of blocks (or actually, a tree when several competing branches exist). Blocks conceptually contain a header and a list of operations, which are specific to the economic protocol.

The header itself decomposes into a shell header (common to all Tezos economic protocols), and a protocol-specific header. The shell header contains protocol-agnostic data such as the predecessor’s block hash and the block’s timestamp.

Context

The state of the blockchain. The context is defined by the economic protocol and typically includes information such as “this account is credited with this many tez” and “this is the code for that smart contract.”

The context is modified by operations. For example, an operation can transfer tez from one account to another, which modifies the part of the context that tracks account credit.

Economic protocol

The economic protocol is the set of rules defining valid operations and blocks, how the network agrees on the next block to build (the consensus algorithm), and how operations update the blockchain state, also called context.

In Tezos, the economic protocol can be upgraded without interruption or forking of the blockchain. This is because the procedure for an upgrade is also defined within the economic protocol, which can thus update itself.

Fitness (a.k.a. score, weight)

For each block, the consensus algotrithm can compute a score called fitness which determines the quality of the chain leading to that block. The shell changes the head of the chain to the valid block that has the highest fitness.

Height

See level.

Level (a.k.a. block height)

The position of a block in the blockchain, that is, the number of blocks since the genesis block, where the genesis block is at level 0.

Mempool

A pool (set) of operations maintained by a node and not yet included in a block.

Metadata

A (block or operation) metadata is a piece of data computed as a result of the application of the block or operation on an associated context. The metadata consists of many pieces of information such as the operation receipts, rewards updates, voting period, etc.

A block’s metadata is the collections of operations metadata for all the operations included in the block (if the validation was successful).

For a detailed metadata content check the Alpha RPCs - Reference under the prefix ../<block_id>/metadata.

Node

A peer in the P2P network. It maintains a local state and propagates blocks and operations.

Operation

An operation transforms the context; this is what makes the state of the chain change. Operations are grouped into blocks; thus, the chain progresses in batches. For the different kinds of operations defined by the protocol, see operation kinds.

Score

See fitness.

Shell

The shell is a software component of the node. It is parameterized by a specific economic protocol. It serves as the bridge between the P2P layer (handling communication between nodes) and the economic protocol layer (handling the context, operation application, scoring, etc.).

Tezos

Used either as a noun or an adjective to designate:

  • An open-source project and software (as in, “contributing to the Tezos protocol”)

  • A peer-to-peer network of nodes maintaining a blockchain (as in “a Tezos node”)

  • The specific Tezos chain with the most economic relevance (as in “the Tezos chain”). In particular, the chain whose millionth block had hash BKtC4QCWoF73kxLj773vFpQuuwrnye6PS7T1aM3XEPvFXiQbNu7

Weight

See fitness.

Protocol terms

Accuser

When a delegate attempts double signing (or when it tries to abuse the network in another similar way), another delegate can make an accusation, by providing evidence of the offense. The delegate injecting the accusation in a newly baked block is called the accuser.

The accuser is awarded some funds from the security deposit of the accused.

When using Octez, accusation operations are emitted by the accuser daemon. Note that this daemon is not associated to a delegate: accusation operations are anonymous, and any delegate can include them in a block.

Account

An account is an address managed by the protocol. In the context, each account is associated with a balance (an amount of tez available).

An account can be either a user account or a smart contract.

Attesting

When a block is created and propagated on the network, delegates that have attesting rights for the matching block level and round can emit an attestation operation. Attestation operations are included in the next block.

Attesting rights

See baking rights.

Baker

When a delegate creates a new block, it is called the baker of this block. Baking rights are distributed to different delegates based on their available stake. Only a delegate with baking rights is allowed to bake. The baker selects transactions from the mempool to be included in the block it bakes.

When using Octez, baking and other consensus actions are handled by the baker daemon, on behalf of one or more delegate accounts. By extension, a baker designates the owner of such a delegate account, typically running the baker daemon on its behalf.

Baking

The act of creating a new block by a baker.

Baking rights

Baking/attesting a block can only be done by a delegate who holds the baking/attesting right for that block level and round. At the start of a cycle, baking and attesting rights are computed for all the block levels and rounds in the cycle, based on the proportion of the stake of each delegate.

For each block level and round, there is exactly one account that is allowed to bake, but several accounts are allowed to attest.

Burn

To ensure responsible use of the storage space on the public blockchain, there are some costs charged to users for consuming storage. These costs are burnt (i.e., the amount of tez is destroyed). For example, a per-byte storage cost is burnt for increasing the storage space of a smart contract; a fixed amount is burnt for allocating a new contract (which consumes space by storing its address on the blockchain).

See also fee.

Constant

Protocols are parameterized by several parameters called protocol constants, which may vary from one protocol to another or from one network to another.

Contract

See account.

Cycle

A cycle is a sequence of consecutive blocks of fixed length (given by a protocol constant). E.g., cycle 12 started at block level 49152 and ended at block level 53248.

Cycles are used as a unit of “time” in the block chain. For example, the different phases in the amendment voting procedures are defined based on numbers of cycles.

The length of a cycle is a (parametric) protocol constant, and thus might change across different Tezos protocols.

Delegate

A user account that can participate in consensus and in governance. Actual participation is under further provisions, like having a minimal stake. A user account becomes a delegate by registering as such. Through delegation, other accounts can delegate their rights to a delegate account. The delegate’s rights are calculated based on its stake. Note that tz4 accounts cannot be delegates.

Delegation

An operation in which an account designates a delegate. The delegating account’s balance increases the delegate’s stake and consequently its baking rights and attesting rights. However, the delegate does not control the funds of the delegating account, e.g., it can not spend them.

Double signing

The situation when a baker signs two different blocks at the same level and same round, is called double baking. Double baking is detrimental to the network and might be indicative of an attempt to double spend. The same goes for signing two different attestations at the same level and the same round. As such, double signing (i.e., double baking or double attesting) is punished by the network: an accuser can provide proof of the double signing to be awarded part of the double signer’s deposit – see Slashing.

Failing Noop

The Failing_noop operation implements a No-op, which always fails at application time, and should never appear in applied blocks. This operation allows end-users to sign arbitrary messages which have no computational semantics.

Fee

To ensure responsible use of computation resources of other nodes, and also to encourage active participation in the consensus protocol, users pay fees to bakers for including their operations in blocks. For example, fees are paid to a baker for operations such as a transaction or a revelation of a public key.

Currently, only manager operations require collecting fees from its sender account.

See also burn.

Gas

A measure of the number of elementary steps performed during the execution of a smart contract. Gas is used to measure how much computing power is used to execute a smart contract.

Implicit account

See user account.

Layer 1

The primary blockchain i.e. the Tezos chain. Within any blockchain ecosystem, Layer 1 (L1) refers to the main chain to which side chains, rollups, or other protocols connect and settle to. The Layer 1 chain is deemed to be most secure, since it has the most value (or stake) tied to it, and be most decentralized and censorship resistant. However, transaction space is limited leading to low throughput and possibly high transaction costs. See Layer 2.

Layer 2

Layer 2 (L2) includes sidechains, rollups, payment channels, etc. that batch their transactions and write to the layer 1 chain. By processing transactions on layer 2 networks, greater scalability in speed and throughput can be achieved by the ecosystem overall, since the number of transactions the layer 1 can process directly is limited. By cementing transactions from a L2 to L1, the security of the L1 chain backs those operations. In Tezos there are a number of layer 2 solutions, including Smart Optimistic Rollups, validity or ZK-Rollups Epoxy , zkChannels, and sidechains such as Deku.

Michelson

The built-in language used by a smart contract.

Minimal stake

An amount of tez (e.g., 6000ꜩ) serving as a minimal amount for a delegate to have baking rights and voting rights in a cycle.

Operation kinds

The main kinds of operations in the protocol are transactions (to transfer funds or to execute smart contracts), accusations, activations, delegations, attestations, and originations. For the full list of operations, see Blocks and Operations.

Originated account

See smart contract.

Origination

A manager operation whose purpose is to create – that is, to deploy – a smart contract on the Tezos blockchain.

Round

An attempt to reach consensus on a block at a given level. A round is represented by an index, starting with 0. Each round corresponds to a time span. A baker with baking rights at a given round is only allowed to bake during the round’s corresponding time span. Baking outside of one’s designated round results in an invalid block.

Roll

deprecated; see minimal stake.

Smart contract

Account which is associated to a Michelson script. They are created with an explicit origination operation and are therefore sometimes called originated accounts. The address of a smart contract always starts with the letters KT1.

Smart Optimistic Rollups

Smart optimistic rollups constitute a layer 2 solution that can be used to deploy either a general-purpose polyvalent layer 2 blockchain (e.g., an EVM-compatible one), or an application-specific DApp. See Smart Optimistic Rollups.

Stake

The amount of tokens that determines a delegate’s weight in the governance process and in the selection of its baking and attesting rights. A delegate’s stake is usually given by the delegate’s own tokens plus the sum of tokens delegated to it. However, there are cases when this is not the case, see here for details.

Staker

A user account that made a security deposit. The user account must have set a delegate. The security deposit accrues to the stake of the user account’s delegate and is subject to slashing in case the delegate misbehaves – see Slashing.

Tez

A unit of the cryptocurrency native to a Tezos chain, such as in “I sent you 2 tez.” Tez is invariable. It is not capitalized except at the beginning of a sentence or when you would otherwise capitalize a noun. See also XTZ.

Transaction

An operation to transfer tez between two accounts, or to run the code of a smart contract.

User account

An account that is linked to a public key. Contrary to a smart contract, a user account cannot include a script and it cannot reject incoming transactions. User accounts are sometimes called “implicit accounts”.

If registered, a user account can act as a delegate.

The address of a user account always starts with the letters tz followed by 1, 2, 3, or 4 (depending on the signature scheme) and finally the hash of the public key. See Accounts and addresses for a more detailed explanation on addresses.

Validation pass

An index (a natural number) associated with a particular kind of operations, allowing to group them into classes. Validation passes enable prioritizing the validation and application of certain classes of operations.

Voting period

Any of the proposal, exploration, cooldown, promotion or adoption stages in the voting procedure when amending the economic protocol.

Voting listings

The list calculated at the beginning of each voting period that contains the staking balance (in number of mutez) of each delegate that owns more than the minimal stake at that moment. For each delegate, the voting listings reflect the weight of the vote emitted by the delegate when amending the economic protocol.

XTZ

XTZ, tez, or ꜩ (\ua729, “Latin small letter tz”) is the native currency of Tezos.

“XTZ” is an ISO-4217-compatible code for representing tez on the most economically relevant Tezos chain. Unless there is a very specific reason to use an ISO code for it, the term tez is preferred. Situations where the ISO code might be useful typically involve accounting systems, exchange rates with other currencies, and anything that might need some sort of standardized code.