Now if the time has elapsed within a given price group, then the fare will go up to the rate of the next price group. So it can pay to make your reservations way in advance. Actually, it would be more accurate to say that airlines distinguish between classes of service and types of fares. The best way to describe it is as a series of overlapping tiers of fares. Standard is practically nonexistent these days.
Fares usually drop with lower class service.