0 a ticket for travel by plane, train, etc. for which you pay less, either by buying it before you travel or because you make your journey during a less busy period:
There is a complex framework of savers, supersavers and awayday tickets.
All the rail companies argue that, by offering advance booking discounted tickets instead of supersavers, they are not penalising passengers, but that is nonsense.
The growth market in discount fares has not stopped some operators putting up the prices in real terms of unregulated cheap day returns, supersavers and similar discounted fares.
If there was no significant differential between a saver and a supersaver, why would any passenger want to buy a supersaver?