Glossary

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.

Tezos

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 Paris 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.).

Weight

See fitness.

Protocol

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 an originated account or an implicit account.

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 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

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. See Accounts and addresses for a more detailed explanation on addresses.

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. Currently, Layer 2 solutions on Tezos are built as smart rollups.

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.
PVM: A PVM (Proof-generating Virtual Machine) is a reference implementation for a device on top of which a smart rollup can be executed. This reference implementation is part of the economic protocol and is the unique source of truth regarding the semantics of rollups. The PVM is able to produce proofs enforcing this truth. This ability is used during the final step of a refutation game.
Refutation game: A process by which the economic protocol solves a conflict between two rollup committers. Note that the refutation mechanism used in Tezos smart rollups corresponds to the notion of fraud proofs used in other blockchain/Layer 2 ecosystems.
Refutation period: When the first rollup commitment for a rollup commitment period is published, a refutation period of two weeks starts to allow this commitment to be challenged.
Roll: deprecated; see minimal stake.
Rollup commitment: A claim that the interpretation of all rollup inbox messages published during a given period, and applied on the state of a parent rollup commitment, led to a given new state by performing a given number of execution steps of the PVM.
Rollup commitment period: A period of roughly 15 minutes during which all rollup inboxmessages must be processed by the rollup node state to compute a rollup commitment. A commitment must be published for each commitment period.
Rollup committer: An implicit account that has published and made a deposit on a rollup commitment.
Rollup inbox: A sequence of messages from the Layer 1 to all the smart rollups. The contents of the inbox are determined by the consensus of the economic protocol.
Rollup node: A daemon required for deploying and operating smart rollups. The rollup node is responsible for making the rollup progress by publishing rollup commitments and by playing refutation games.
Rollup outbox: A sequence of messages from a smart rollup to the Layer 1. Messages are smart contract calls, potentially containing tickets. These calls can be triggered only when the related rollup commitment is cemented (hence, at least two weeks after the actual execution of the operation).

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.
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 Rollup: Smart 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: An implicit account that made a security deposit. The implicit account must have set a delegate. The security deposit accrues to the stake of the implicit account’s delegate and is subject to slashing in case the delegate misbehaves – see Slashing.
Transaction: 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 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.