Its appearance when attached resembles the nunchaku, hence the name. It features an analog stick similar to the one found on the GameCube controller and two trigger buttons. It works in tandem with the main controller in many games. Like the Wii Remote, the Nunchuk also provides a three-axis accelerometer for motion-sensing and tilting, but without a speaker, a rumble function, or a pointer function.
Source: Wikipedia, "Wii Remote," available under the CC-BY-SA License.