Confirmation means proving that something is true or correct, or receiving proof that something you believed or expected is actually right. When a scientist runs an experiment three times and gets the same result each time, that's confirmation that their hypothesis works. When you email a teacher asking if there's homework and she writes back “yes, pages 10-15,” her reply is confirmation of the assignment.

The word carries a sense of removing doubt or uncertainty. Before confirmation, you might wonder or suspect something; after confirmation, you know for sure. A doctor might order a second test to get confirmation of a diagnosis. A family planning a trip calls the hotel for confirmation that their reservation is ready.

In some religious traditions, Confirmation (with a capital C) names a ceremony where young people confirm their faith and commitment to their church community, often around age 12-14. This builds on an earlier idea: you're making official and certain something that was previously developing or uncertain.

The verb form is confirm. When you confirm plans with a friend, you're making sure they're still happening. When evidence confirms a theory, it proves the theory correct.