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What is a crypto transaction?
A transaction is a signed instruction from a wallet that changes the state of a blockchain, such as sending coins or calling a smart contract. The signature, made with the sender's private key, proves the owner authorised it. Once it is included in a block, the network treats it as part of the shared record.
What it means for you
A transaction cannot be recalled once it is included in a block, so the recipient address and amount you sign are what happens. Every transaction pays a network fee, even a small one, and a block explorer shows its status and fee.
A common mistake: “If I send to the wrong address, the network can reverse it.”
In fact: No one on the network can reverse an included transaction. As bitcoin.org puts it, a Bitcoin transaction can only be refunded by the person who received the funds; the same holds on other public chains.
How it works
An Ethereum transaction carries a sender, a recipient, a value in wei (1 ETH is 10^18 wei), optional input data for a contract call, a nonce, a gas limit, and two fee caps: a maximum tip for the validator and a maximum total fee per unit of gas. The sender's private key signs it, a transaction hash is generated, and it is broadcast to the network's transaction pool. A validator includes it in a block, and that block is later justified and then finalized. A simple ETH transfer uses 21,000 units of gas.
Sources: ethereum.org: Transactions, bitcoin.org: Some things you need to know · checked 4 October 2026
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