Transaction
blockchain · technical
A serialized state transition that a blockchain can validate, relay, and include in a block.
A transaction proposes a change to blockchain state. Most user transactions include cryptographic authorization, but the exact structure depends on the protocol; a proof-of-work coinbase transaction, for example, creates the permitted block subsidy without an ordinary sender signature.
In a UTXO system, a transaction consumes named outputs and creates new outputs. In an account system, it commonly changes balances, nonces, and contract storage. Nodes independently check the applicable consensus and local relay rules.
A relayed transaction may enter a node's mempool before a miner includes it in a block. Inclusion gives it one confirmation; later blocks increase the cost of reorganizing that history. Unconfirmed transactions can be dropped, conflicted, or replaced according to network policy.
Related terms
Mempool
→A node's local set of unconfirmed transactions accepted for possible relay and block inclusion.
blockchain · node
Block
→A batch of valid transactions added to a blockchain, linked to the previous block by a cryptographic hash.
mining · blockchain · security
Confirmations
→The count of blocks confirming a transaction, usually including the block that first contains it.
security · blockchain
Transaction Fee
→The amount paid to miners or validators for including a transaction and consuming scarce block space or execution resources.
blockchain · technical · basics
Unspent Transaction Output (UTXO)
→A discrete spendable output on a UTXO blockchain, similar to a digital coin that must be spent whole.
technical · blockchain