This glossary is divided in two sections, the first one concerns Tezos, and the second one concerns the Alpha protocol, which is the current economic protocol.



A block is a collection of several Operations. The operations are located in the payload of the block which is specific to the Economic Protocol.

Along with the payload, the block includes a header which contains protocol-agnostic data. It consists of generic information 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.


See score.


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.

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

The score is a metric used to compare contexts. For example, when several blocks claim to be heads of the chain, their context’s scores are compared. The highest scoring block is selected as the head of the chain.


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 score.

Protocol Alpha


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.

Using the tools provided by Nomadic Labs, accusation is handled by a separate binary.


An account is a unique identifier within protocol Alpha. 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.

Using the tools provided by Nomadic Labs, baking is handled by a separate binary.

Baking/Endorsement rights

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

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.


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 endorsement rights. The Baking rights and Endorsement 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 rolls 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 Endorsement rights for the matching block height can emit an endorsement operation. The accounts that emit the block are the endorsers of the block. The endorsement operations can be included in the next block to increase the block’s Score.

Using the tools provided by Nomadic Labs, endorsement is handled by a separate binary.


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.


In protocol Alpha, the main operations 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., 8000ꜩ) serving as a unit to determine delegates’ baking rights in a cycle. A delegate with twice as many rolls as another will be given twice as many rights to bake.

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.