Huddle is the name given to the large circle-like formation taken by the players on the field prior to the start of the play. This is where the quarterback (offense) or linebacker (defense) tells the rest of the players which play will be run.
There are several different people who have been credited with the invention of the huddle. One of the earliest is Gallaudet University quarterback Paul D. Hubbard who, in 1892, "huddled his players up" to prevent the other team from being able to read his hand signals. This became a common strategy to prevent the other team from knowing which play you would use. In the 2000s Peyton Manning and the Indianapolis Colts began using something called a "muddle huddle"--this is a less formal huddle that does not take as much time, and it is used to prevent the defense from having enough time to huddle up or make substitutions.