Transaction
A signed data message that asks a blockchain to transfer value, execute code, or update state.
A transaction is the basic message users submit to a blockchain. Nodes verify that it follows consensus and policy rules, then miners or validators may include it in a block so it becomes part of the chain's history.
Transaction structure depends on the accounting model. UTXO chains consume previous outputs as inputs and create new outputs, while account-based chains update balances and may execute contract code.
A typical transaction is created, signed, broadcast, stored temporarily in mempools, included in a block, and then gains confirmations as more blocks build on top. Before confirmation, it may be replaced, dropped, or conflicted depending on network rules.
Transactions are usually tracked by a transaction ID, but pre-confirmation behavior can matter. Some historical malleability issues allowed IDs to change before confirmation, and some networks allow fee-bumping or replacement policies.
Related terms
9 linkedExplore connected entries beyond the alphabetical index.
Block
→A batch of valid transactions added to a blockchain, linked to the previous block by a cryptographic hash.
Mempool
→A temporary storage space in a node for pending transactions that have not yet been included in a confirmed block.
Confirmations
→The count of blocks confirming a transaction, usually including the block that first contains it.
Fee
→A transaction fee is the amount paid for block inclusion, compensating block producers and discouraging spam.
Unspent Transaction Output (UTXO)
→A discrete spendable output on a UTXO blockchain, similar to a digital coin that must be spent whole.
P2PKH
→A common script type where the output can be spent by proving knowledge of the private key corresponding to a hashed public key.
P2SH
→A script type where the output is locked to the hash of a redeem script, enabling features like multi-sig.
OP_RETURN
→An opcode in Bitcoin's scripting language that allows data to be written onto the blockchain, while marking the output as unspendable.
Transaction ID (TXID)
→A transaction's unique identifier, usually derived by hashing its serialized contents according to the chain's rules.
All terms and definitions may update as the Cryptionary improves.
