This is the 1772nd most frequent French word.
confirmer
To confirm.
The verb 'confirmer' is used in its literal sense, meaning 'to validate or make official' a reservation in this context.
Je vais confirmer ma réservation demain.
I will confirm my reservation tomorrow.
Here, 'confirmer' indicates the act of stating definitively or affirming an intention or plan, as applied to a social event participation.
Elle a confirmé qu'elle viendrait à la fête.
She confirmed that she would come to the party.
In this sentence, 'confirmer' refers to providing evidence or support for the correctness of an idea or supposition.