Учебник английского языка «Survival English»
Culture File 38:
Open tickets cost you more. All First and Business class tickets are open, i.e. you can change your flight times. Full-fare Coach / Economy tickets are usually open.
Cheaper tickets are usually Restricted, i.e. you can’t change them. The best-known type is APEX (Advance Purchase Excursion).
Often you have to stay overnight — something most business travelers won’t want to do! it’s also cheaper if you stay over on a Saturday night for the same reason.
In the U.S.A., it’s cheaper to travel at off peak times. Flights on Monday mornings and Friday afternoons are the most expensive.