Swallowtail (flag)

Swallowtail flag shape.
A barn swallow in flight. Note the shape of its tail.

In flag terminology, a swallowtail is either

  1. a V-shaped cut in a flag that causes the flag to end in two points at the fly; or
  2. any flag that has this V-shaped cut.

The name comes from the forked tail that is a common feature of the swallow species of birds.