Double coverage

In American and Canadian football double coverage is a state of defensive playcalling wherein two defensive players are assigned to "cover" one offensive player. This situation is often seen with standout wide receivers and running backs.

It is extremely rare to have 2 DBs man-cover a single receiver. Commentators who use the term "double-coverage" almost always mean a CB covering a WR man-to-man, with a safety playing "over the top" (typically trying to stay in front of the WR's route) for deep ball assistance.