What is Bitcoin confirmation?

2017-08-29 00:00:00:

The recipient of Bitcoin immediately after receipt has no opportunity to spend them. This is because, as soon as the sender sends to the recipient, the transaction is sent to the network to be included in a block in order to become legitimate. It is this process of including a transaction in a block that is called confirmation. Once the transaction is confirmed, Bitcoin coins can be used further. As a rule, confirmation takes 10-40 minutes, but the confirmation speed depends on the load on the bitcoin network itself and in rare cases can take up to several days.