A confirmation is a way of measuring how settled a crypto transaction is. When your transaction is first included in a block, it has one confirmation. Each additional block added after that counts as another confirmation, gradually making the transaction more permanent.
The reason confirmations matter is security. Reversing a transaction would mean rewriting the block it sits in and every block after it, which grows harder with each new block. So a transaction with many confirmations is far more difficult to undo than one with just a single confirmation.
Different services wait for different numbers of confirmations before treating a transaction as final. A small payment might be accepted quickly, while a large one may wait for several confirmations to be safe. How long this takes depends on the network block time, which varies from seconds on some chains to about ten minutes on Bitcoin.
