While some of the drills at the NFL Scouting Combine are foreign outside of the football world, the bench press is not one of them. Most who have gone through a high school gym class have likely participated in the bench press. The difference between the average person and the 335 prospects at the combine is weight and a lot of it.
Players will set up with 225 pounds, including the bar, and attempt to complete as many consecutive repetitions as possible. It's a way for players -- especially offensive and defensive linemen -- to show off their upper-body strength. Upper-body strength is important for players in the trenches as they use that strength to block or rip away from offensive linemen on every play.
While the bench press is a measure of strength, it's also a measure of muscle endurance. Many players will complete 20 or more repetitions with other players and coaches cheering them on. It's important to factor in body type with the final repetition number. Players with long arms are at a disadvantage in the drill as they have to lift the weight a longer distance. Just because an offensive lineman fails to put up a lot of reps doesn't mean he lacks the strength to play in the NFL. A lineman with long arms will typically complete fewer reps than a lineman with short arms. A lot of reps from a lineman with long arms can thus be even more impressive.
Over the years, some have put on impressive shows, none more than Justin Ernest, who threw up 51 reps back in 1999. More recently, Chicago Bears defensive tackle Stephen Paea did 49 reps, the second-highest total in combine history.