System Administration Guide: Naming and Directory Services (NIS+)

Password will expire Message

If you receive a Your password will expire in N days message (where N is a number of days), or a Your password will expire within 24 hours message, it means that your password will reach its age limit and expire in that number of days (or hours).

In essence, this message is telling you to change your password now. (See Changing Your NIS+ Password.)