Single is a way to take an 8-dancer call and make it a 4-dancer call; or to take a 4-dancer call and make it a 2-dancer call.

In the Single version of a call, each dancer executes the movement that would normally be done by a set of two dancers within the normal version of the call. Hence, for a call to have a Single version, it must be possible to group all dancers into sets of two, in which the dancers in each set are always facing the same direction throughout the given call. The dancers in each set are usually dancing their portion of the call As Couples, In Tandem, Once Removed, or Twosome (or some combination of these concepts).

You can think of Single as replacing each set of two dancers with a single dancer located exactly half-way between the two dancers. This single dancer then executes the given call always staying on a path located exactly half-way between where the two dancers would be in the normal version of the call.