Airline ticket of international of a lot of indulgence has a few to limit a condition, common have:

Cannot sign turn: Point out to airline cannot be changed after the ticket.
Cannot change the date: After pointing out a ticket, cannot change set out or return trip date. (airline of specific according to sets)
Cannot return a ticket: Point out to return trip ticket or all airline ticket cannot be cancelled after the ticket. (airline of specific according to sets)