A standing permission allowing a named contract address to move a specified amount of one of your tokens, at any time, until the permission is changed or exhausted.
Why it matters
An approval is not consumed by the transaction that created it. Interfaces commonly request an unlimited allowance, which covers your entire balance of that token — including tokens acquired later. Approvals are public on-chain data and can be inspected in any block explorer. See how to check what your wallet has approved.
Not advice. Definitions are for understanding, not instruction. Nothing here is financial, legal, tax or security advice.