"Piggy Back" connectors are more simply a "Fast Tab" connector, but with the "Female" side, it has a "Male" end attached to it. These were made so people wouldn't have to struggle with fitting two wires into one connection, or so they don't have to make another connection just for one more wire. With the same dependability as the standard fast tabs, they have many uses, and have fast become part of the solder-less connection world.