In American football and Canadian football, defensive backs (DBs) are the players on the defensive team who take positions somewhat back from the line of scrimmage; they are distinguished from the defensive line players and linebackers, who take positions directly behind or close to the line of scrimmage.^[1]

The defensive backs, in turn, generally are classified into several different specialized positions:

• Safety: Free safety – most often the deepest safety Strong safety – the bigger more physical safety, much like a small, quicker linebacker
• Defensive halfback (Canadian football only)
• Cornerback – which include: Nickelback – the fifth defensive back in some sets, such as the nickel formation Dimeback – the sixth defensive back in some sets, such as the dime formation The seventh defensive back, in the exceedingly rare "quarter" set, but often strong known as a dollar back or a quarter back (not to be confused with the offensive player who throws the ball)

The group of defensive backs is known collectively as the secondary; being the second line of defense after the lineman and guards.^[2] They most often defend the wide receiver corps; however, at times they may also line up against a tight end or a split out running back.