Nose Tackle: In a 3-4 defense (three linemen, four linebackers), the nose tackle is the middle lineman who lines up over the offensive center.
Onside Kick: When the kicking team attempts to get the ball back during the kickoff by tapping a short kick. The kicking team can get the ball back only if the kick goes more than 10 yards, so kickers often practice kicking the ball into the ground and forcing a big bounce that covers the 10 yards and gives the kicking team a chance to gain possession.
Pass Interference: When a defensive player unfairly interferes with a receiver's attempt to catch the football. There is also offensive pass interference, when a receiver unfairly interferes with a defender's attempt to intercept a pass.
Quarterback: The player directly behind the offensive line who usually takes the snap and manages the offense. The quarterback is considered the most important player on a football team.
Red Zone: The area between the 20-yard line and the end zone, generally on the side of the field where the offense is trying to score.
Super Bowl: Perhaps the world's most famous football game, which determines the annual champion of the NFL. The Super Bowl is generally played in January or February and is widely considered the most popular sporting event in the United States.
Two-Minute Warning: When two minutes are remaining in each half, officials will stop play for teams to regroup. This has the same effect as a timeout, but it is built into the game and neither team has to use one of their three timeouts to stop play.
Unsportsmanlike Conduct: A penalty that's given when a player or team is acting unethically according to the official's judgment. It is often used to penalize excessive touchdown celebrations, but can also be called for on-field fights and other incidents.
Video Replay: In the NFL and high-level college football, officials can occasionally use replay to determine if the correct call was made on a controversial play. Video replays can be requested by the officials or by head coaches depending on the situation.
Wideout: Another term for a wide receiver, or a player who's job is to catch forward passes thrown by the quarterback.
X-Receiver: A wide receiver that lines up on the line of scrimmage out wide, often on the weak side. The terms "X" "Y" and "Z" receivers are generally used only in play calling, and are just considered "wide receivers" to outsiders.
Yard Line: The amount of distance from the nearest end zone. The 50-yard line is considered the middle of the field, and all other yard lines correspond with whatever end zone they're closest to.
Zone Defense: When a defender is responsible for a certain area of the field in pass coverage, rather than a certain offensive player.