This glossary is divided in two sections, the first one concerns Tezos, and the second one concerns the economic protocol. The definitions in the latter section may be different for other protocol versions.



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 protocols) and a protocol-specific header. The shell header contains protocol-agnostic data such as the block predecessor’s hash and the block’s timestamp.


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 application that runs on top of the blockchain proper. It defines a Context (the state of the application), some Operations (how the state evolves).

In Tezos, the economic protocol can be upgraded without interruption or forking of the blockchain. The procedure for an upgrade is defined within the economic protocol itself so it can be upgraded as well.

Fitness (a.k.a. Score, a.k.a. Weight)

To each block, we associate a fitness which determines the quality of the chain leading to that block. This measure is computed by the consensus protocol. The shell changes the head of the chain to the valid block that has the highest fitness.


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


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


A metadata, or operation’s metadata, is a piece of data associated to an Operation. It is computed as a result of the application of the operation included in a Block on its associated Context. The metadata consists in many 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 RPCs - Index under the prefix ../<block_id>/metadata.


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


Operations transform the context, this is what makes the state of the chain change. Operations are grouped into blocks so that the chain progresses in batches.


See fitness.


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.).


See fitness.



When a node attempts to inject several incompatible blocks (or when it tries to abuse the network in another similar way), another node can make an accusation: show evidence of attempted abuse. The node making the accusation is the accuser.

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

When using Octez, accusations are handled by a separate binary.


An account is a unique identifier within the protocol. There are different kinds of accounts (see Originated account and Implicit account).

In the Context, each account is associated with a balance (an amount of tez available).


When a node creates a new block, it is the baker of this block. Baking rights are distributed to different accounts based on their available balance. Only a node that handles an account with baking rights is allowed to bake; blocks created by another node are invalid. The baker selects transactions from the mempool to be included in the block it bakes.

When using Octez, baking is handled by a separate binary.

Baking/Endorsing rights

A delegate is allowed to bake/endorse a block if he holds the baking/endorsing right for that block. At the start of a Cycle, baking and endorsing rights are computed for all the block heights in the cycle, based on the proportion of Rolls owned by each account.

For each block height, there are several accounts that are allowed to bake. These different accounts are given different Priorities.

For each block height, there are several accounts that are allowed to endorse. There can be multiple endorsements per block.


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.


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


See account.


A cycle is a set of consecutive blocks. E.g., cycle 12 started at block height 49152 and ended at block height 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 cycles.


An Implicit account to which an account has delegated their baking and endorsing rights. The baking rights and endorsing rights are calculated based on the total balance of tez that an account has been delegated to.


An operation in which an account balance is lent to a delegate. This increases the delegate’s stake and consequently its Baking rights. The delegate does not control the funds from the account.

Double baking

When a baker signs two different blocks at the same height, it is called double baking. Double baking is detrimental to the network and might be indicative of an attempt to double spend. As such, it is punished by the network: an accuser can provide proof of the double baking to be awarded part of the baker’s deposit.


When a block is created and propagated on the network, nodes that have endorsing rights for the matching block height can emit an endorsement operation. The accounts that emit the block are the endorsers of the block. Endorsement operations are included in the next block.

When using Octez, endorsing is handled by a separate binary.


To ensure responsible use of computation resources of other nodes, and also to encourage active participation in the consensus protocol, there are some fees that users pay 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.

See also Burn.


A measure of the number of elementary operations 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

An account that is linked to a public key. Contrary to a smart contract, an Implicit account cannot include a script and it cannot reject incoming transactions.

If registered, an Implicit account can act as a delegate.

The address of an Implicit account always starts with the letters tz followed by 1, 2 or 3 (depending on the signature scheme) and finally the hash of the public key.


The built-in language used by a smart contract.


The main operations in the protocol are transactions (to transfer funds or to execute smart contracts), accusations, activations, delegations, endorsements and originations.

Originated account

See smart contract.


An operation to create a smart contract.


A rank of different baking rights. Each rank corresponds to a time span. A baker with baking rights at a given priority is only allowed to bake during the priority’s corresponding time span. Baking outside of one’s designated priority, results in an invalid block.


An amount of tez (e.g., 6000ꜩ) serving as a minimal amount to determine delegates’ baking rights in a cycle. A delegate with twice as much stake as another will be given twice as many rights to bake. A roll also serves as a unit to determine delegates’ voting rights in a cycle.

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.


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

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 rolls) of each delegate that owns more than one roll at that moment. For each delegate, The voting listings reflects the weight of the vote emitted by the delegate when amending the economic protocol.