What does advance purchase fare mean?

advance purchase fare meaning in Law Dictionary

guarantee that a ticket will likely to be issued days just before travel. Relate to APEX fare.

advance purchase fare meaning in Business Dictionary

that will require the ticket is granted a specific number of days before departure or within a fixed time from time of booking. In effect, all airline fares (and airport taxes) are subject to change-up towards the time a ticket is issued (however afterwards). See also APEX fare.