Swingers are people who engage in recreational social activities, often involving sexual activity. The term can refer to couples who swing, or to single people who engage in such activities. Pendulums are objects that hang from a fixed point and swing back and forth due to gravity. DOORS are structures used to open and close an entrance to a room or building. HEPCATS are slang for people who are fashionable and up-to-date with the latest trends. All of these terms can be related to swingers, as they all involve movement and/or fashion.