This command is used by several commands as a way to confirm changes made to your account.
This is most commonly used to confirm your email address once you register or change it.
This is also used after the RESETPASS command has been used to force identify you to your nick so you may change your password.
Additionally, Services Operators with the nickserv/confirm permission can replace passcode with a users nick to force validate them.
Syntax: CONFIRM passcode