Preseasons

In all 3 major professional sports, the preseason consists of two phases:

Preseason is called Spring Training in baseball.
It includes a series of practices and exhibition games before the start of the regular season
Teams hold training camps in the states of Arizona and Florida, where the early warm weather allows teams to practice and play without worrying about late winter cold.
Spring Training typically lasts almost two months, starting in mid-February and running until just before the season-opening day, traditionally the first week of April.

Each NFL team is required to schedule three preseason games which start in August and last for 3 weeks.
Prior to the exhibition games the teams hold Training Camp at an off-site location. Training Camps are a time for NFL coaches and staff to see how new rookies and veterans perform. It is also time to get everyone back into football shape.

Following the summer break, teams begin training camps in late September. Training camps allow the coaching staff to evaluate players (especially rookies), scout the team’s strengths and weaknesses, prepare the players for the rigorous regular season and determine the 12-man active roster (and a 3-man inactive list) with which they will begin the regular season.
After training camp, a series of preseason exhibition games are held.