A half-round metal strip bent into a pin whose ends can be flared after insertion through a slot or hole.
A split pin that is secured (after passing through a hole) by splitting the ends apart. cotter-pin

A slender prong. Pins are commonly encountered as the contacts protruding from a male connector. Connectors are often identified by the number of pins they have. Other types of pins are the spidery, leglike metal appendages that connect computer chips to sockets on a circuit board or directly to the circuit board. See the illustration.