In American football, a nickel defense (also known as a 4–2–5 or 3–3–5) is any defensive alignment that uses five defensive backs, of whom the fifth is known as a nickelback. The original and most common form of the nickel defense features four down linemen and two linebackers.

The nickel defense means there are 5 defensive backs on the field. Nickel defenses are used on 3rd downs when the defense is expecting the offense to throw the football. Dime & quarter defenses have 6, and 7 defensive backs on the field to protect against deep passes or Hail Mary throws.