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.

Note: It is actually extremely rare to nonexistent 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.