In Football, a period is another name for a quarter. In Football, there are four quarters that make up the game, each 15 minutes long. They are called the 1st quarter, the 2nd quarter, the 3rd quarters, and the 4th quarter. After the 2nd quarter is a period called halftime where both teams take a break from the game to rest, as well as strategize. After the 4th quarter, the game is over unless the score is tied, in which case the game has an extra period called overtime.
A clock keeps track of the time left in each period. The clock is displayed in the football stadium, and it is televised for at-home viewers.
An overtime period is a 10 minute additional period during regular season games that is added if the game ends in a tie. If after the 10 minutes the score is still tied, the game ends in a tie.
Although each quarter is only 15 minutes long, the average football game can last over 3 hours. This is because there are many stoppages of play during a game, like timeouts, fouls, if a ball goes out of bounds and even when the quarterback throws an incomplete pass.