A way to snap the fingers where, at the beginning of the snap, your hand is directly in front of you and, by the end of the snap, your hand has been swung (or 'waved') toward the outside. (For example, the right hand is swung toward the right). The swing and snap are simultaneous.
Sometimes (usually?) done the the other hand placed on the hip. This snap is done particularly well by gay people. Thus the name. NOTE: not usually a snap used to accompany music but rather, to emphasize a point.
"Girl! Just LOOK at this apartment! You couldn't even clean it was a tactical nuclear weapon! You're gonna need a genie to just (fabulous faggot backhand-snap, here) snap his fingers, to clean this mess!"