Each Bitcoin transaction is broadcast to all nodes, or computers, Using the Bitcoin client. When the miners confirm a block, a page in the Bitcoin ledger is published attesting that the transactions in that block are valid and that no attempt has been made to spend those bitcoins on two or more things at the same time. This protocol is known as a "confirmation" and occurs every ten minutes, on average.
Transactions become effective after they have been referenced in a block, which serve as a official record of executed transactions. Transactions may only be listed in a block if they satisfy such conditions as valid timestamping and absence of double spending.
One confirmation is considered secure. Having 6 confirmations is considered proof that there is statistically no change that any cheating has occurred.
Malone, J.A (2015). Glossary of Bitcoin Terms and Definitions. United States: Lulu Press, Inc