Nonce

• In the account model, a counter attached to each sending address: every transaction must carry the next number in sequence, which fixes the order of an address’s transactions and prevents the same signed transaction from being executed twice. A pending transaction can be replaced by broadcasting another one with the same nonce and a higher fee, which is how transactions are cancelled or accelerated, and how sweeper bots and rescue attempts compete for the same funds.

The nonce reveals how many transactions an address has sent; contract addresses keep a separate nonce for the contracts they create. The term is also used, with a different meaning, for the value miners vary in Proof-of-Work blocks.