There are 256 NFL games played over a period of 17 weeks in a regular season. Each team plays 16 games and is given a bye week where they are not playing. This bye week is drawn randomly at the start of each season.
In the 1920s after the NFL was starting out, there was no set schedule. Teams played as few as nine games and as many as 16. From the late 1920s to 1946, teams played 11 to 15 games each regular season.
As time passed, the NFL started developing a set schedule for the season. From 1947 to 1960, teams were scheduled for 12 games each season. From 1961 to 1977. the teams played 14 games each season. The leagues changed the schedule in 1978 to 16 games per team over 16 weeks.
The bye week was not introduced into the game until 1990. It allowed teams to have a weekend off through a rotation process, thus creating the need for the 17 week season.
There have been talks about expanding the current football season from 16 games per team to 17 or even 18 games. This would create the need to increase the football season from 17 to 18 or 19 weeks in order to accommodate the teams' bye weeks.