GPIO

A powerful feature of the Raspberri Pi is the row of GPIO (general-purpose input/output) pins along the top edge of the board. The GPIO pins are one way in which the Raspberry Pi can control and monitor the outside world by being connected to electronic circuits.

The Pi can control LEDs, turning them on or off, drive motors, and interact with many other objects. It can also detect the pressing of a switch, change in temperature, or light, etc. by attaching different kind of sensors.

The GPIO application is more for the technically inclined as the user will have to connect relays with jumper wires to the Raspberri Pi whilst still ensuring that they adhere to all the safety standards.

https://www.raspberrypi.org/documentation/usage/gpio