1) A pin is a pronged contact as part of a signal interface in a computer or other communications device. Pins are part of a male connector and plug into a female connector. The number of pins in a connector is sometimes used in describing the connector (for example, "a 25-way D-type connector"). The description of the signal associated with each pin is called the pinout.
2) A PIN is a personal identification number. PINs are commonly assigned to bank customers for use with automatic cash dispensers. They are also used, sometimes with a security token, for individual access to computer networks or other secure systems.