any of various devices in which mechanical parts engage to fasten but usu not to lock something, e.g.:
a fastener, e.g. for a gate, with a pivoted bar that falls into a notch on the gatepost
a fastener, e.g. for a door, in which a spring slides a bolt into a hole
in electronics, a circuit that is held in a particular state until a time signal is given which may change its state