Like an account at a traditional bank, a Solana account may hold funds called [lamports](#lamport). Like a file in Linux, it is addressable by a key, often referred to as a [public key](#public-key-pubkey) or pubkey.
The result of interpreting all programs on the ledger at a given [tick height](#tick-height). It includes at least the set of all [accounts](#account) holding nonzero [native tokens](#native-token).
A contiguous set of [entries](#entry) on the ledger covered by a [vote](#ledger-vote). A [leader](#leader) produces at most one block per [slot](#slot).
The Solana program that owns and loads [BPF](developing/on-chain-programs/faq#berkeley-packet-filter-bpf) smart contract programs, allowing the program to interface with the runtime.
Some number of [epochs](#epoch) after [stake](#stake) has been deactivated while it progressively becomes available for withdrawal. During this period, the stake is considered to be "deactivating". More info about: [warmup and cooldown](implemented-proposals/staking-rewards.md#stake-warmup-cooldown-withdrawal)
A call from one smart contract program to another. For more information, see [calling between programs](developing/programming-model/calling-between-programs.md).
A preimage resistant [hash](#hash) over the final contents of an entry, which acts as the [entry's](#entry) globally unique identifier. The hash serves as evidence of:
The fee account in the transaction is the account that pays for the cost of including the transaction in the ledger. This is the first account in the transaction. This account must be declared as Read-Write (writable) in the transaction since paying for the transaction reduces the account balance.
The smallest contiguous unit of execution logic in a [program](#program). An instruction specifies which program it is calling, which accounts it wants to read or modify, and additional data that serves as auxiliary input to the program. A [client](#client) can include one or multiple instructions in a [transaction](#transaction). An instruction may contain one or more [cross-program invocations](#cross-program-invocation-cpi).
A sequence of [validator](#validator) [public keys](#public-key-pubkey) mapped to [slots](#slot). The cluster uses the leader schedule to determine which validator is the [leader](#leader) at any moment in time.
A list of [entries](#entry) containing [transactions](#transaction) signed by [clients](#client).
Conceptually, this can be traced back to the [genesis block](#genesis-block), but an actual [validator](#validator)'s ledger may have only newer [blocks](#block) to reduce storage, as older ones are not needed for validation of future blocks by design.
A [hash](#hash) of the [validator's state](#bank-state) at a given [tick height](#tick-height). It comprises a [validator's](#validator) affirmation that a [block](#block) it has received has been verified, as well as a promise not to vote for a conflicting [block](#block) \(i.e. [fork](#fork)\) for a specific amount of time, the [lockout](#lockout) period.
A type of [client](#client) that can verify it's pointing to a valid [cluster](#cluster). It performs more ledger verification than a [thin client](#thin-client) and less than a [validator](#validator).
The structured contents of a [transaction](#transaction). Generally containing a header, array of account addresses, recent [blockhash](#blockhash), and an array of [instructions](#instruction).
Learn more about the [message formatting inside of transactions](./developing/programming-model/transactions.md#message-format) here.
A weighted [credit](#credit) in a rewards regime. In the [validator](#validator) [rewards regime](cluster/stake-delegation-and-rewards.md), the number of points owed to a [stake](#stake) during redemption is the product of the [vote credits](#vote-credit) earned and the number of lamports staked.
The executable code that interprets the [instructions](#instruction) sent inside of each [transaction](#transaction) on the Solana. These programs are often referred to as "[_smart contracts_](./developing//intro/programs.md)" on other blockchains.
A stack of proofs, each of which proves that some data existed before the proof was created and that a precise duration of time passed before the previous proof. Like a [VDF](#verifiable-delay-function-vdf), a Proof of History can be verified in less time than it took to produce.
The prioritization fee is calculated by multiplying the requested maximum compute units by the compute-unit price (specified in increments of 0.000001 lamports per compute unit) rounded up to the nearest lamport.
Fee paid by [Accounts](#account) and [Programs](#program) to store data on the blockchain. When accounts do not have enough balance to pay rent, they may be Garbage Collected.
See also [rent exempt](#rent-exempt) below. Learn more about rent here: [What is rent?](../src/developing/intro/rent.md).
Accounts that maintain more than 2 years with of rent payments in their account are considered "_rent exempt_" and will not incur the [collection of rent](../src/developing/intro/rent.md#collecting-rent).
A [block](#block) or [slot](#slot) that has reached maximum [lockout](#lockout) on a [validator](#validator). The root is the highest block that is an ancestor of all active forks on a validator. All ancestor blocks of a root are also transitively a root. Blocks that are not an ancestor and not a descendant of the root are excluded from consideration for consensus and can be discarded.
A 64-byte ed25519 signature of R (32-bytes) and S (32-bytes). With the requirement that R is a packed Edwards point not of small order and S is a scalar in the range of 0 <= S <L.
A past [slot](#slot) that did not produce a [block](#block), because the leader was offline or the [fork](#fork) containing the slot was abandoned for a better alternative by cluster consensus. A skipped slot will not appear as an ancestor for blocks at subsequent slots, nor increment the [block height](terminology#block-height), nor expire the oldest `recent_blockhash`.
Collectively, slots create a logical clock. Slots are ordered sequentially and non-overlapping, comprising roughly equal real-world time as per [PoH](#proof-of-history-poh).
A system [account](#account). [Sysvars](developing/runtime-facilities/sysvars.md) provide cluster state information such as current tick height, rewards [points](#point) values, etc. Programs can access Sysvars via a Sysvar account (pubkey) or by querying via a syscall.
One or more [instructions](#instruction) signed by a [client](#client) using one or more [keypairs](#keypair) and executed atomically with only two possible outcomes: success or failure.
The first [signature](#signature) in a [transaction](#transaction), which can be used to uniquely identify the transaction across the complete [ledger](#ledger).
The number of [confirmed blocks](#confirmed-block) since the transaction was accepted onto the [ledger](#ledger). A transaction is finalized when its block becomes a [root](#root).
A full participant in a Solana network [cluster](#cluster) that produces new [blocks](#block). A validator validates the transactions added to the [ledger](#ledger)
A function that takes a fixed amount of time to execute that produces a proof that it ran, which can then be verified in less time than it took to produce.
Some number of [epochs](#epoch) after [stake](#stake) has been delegated while it progressively becomes effective. During this period, the stake is considered to be "activating". More info about: [warmup and cooldown](cluster/stake-delegation-and-rewards.md#stake-warmup-cooldown-withdrawal)