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 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.


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.


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.


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 Mumbai RPCs - Reference under the prefix ../<block_id>/metadata.


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


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.


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

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

When using Octez, accusations are handled by the accuser 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 delegate 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 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 binary.

Baking/endorsing rights

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

For each block level and block round, there is exactly one account that is allowed to bake.

When a block is created and propagated on the network, delegates that have endorsing rights for the matching block level can emit an endorsement operation. Endorsement operations are included in the next 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 level 49152 and ended at block level 53248.

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

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


An implicit account to which an account has delegated their rights to participate in consensus (aka baking rights) and in governance. The delegate’s rights are calculated based on its own tokens plus the sum of tokens delegated to it. Note that since tz4 accounts cannot be delegates.


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 signing

The action of a baker signing 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 endorsements at the same level and the same round.

Double signing (i.e. double baking or double endorsing) 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.


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 (some of) 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.


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`, `3` or `4` (depending on the signature scheme) and finally the hash of the public key.

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 TORUs (Transaction Optimistic Rollups), Smart Optimistic Rollups, validity or ZK-Rollups Epoxy , zkChannels, and sidechains such as Deku.


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 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, endorsements and originations.

Originated account

See smart contract.


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


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.


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.


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

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 one roll at that moment. For each delegate, the voting listings reflect the weight of the vote emitted by the delegate when amending the economic protocol.