Remote controls, available for digital single lens reflex cameras and some compacts, allow you to take pictures away from the camera. This is useful for portrait or group shots were the photographer wishes to be in the picture. It is also useful when using the camera on a tripod for shots where vibrations, which cause camera shake, needs\ to be avoided at all costs.
There are two types of remotes available for digital single lens reflex cameras, wired and wireless.
Wired remote controls
Wired remotes have been available for single lens reflex cameras for a long time. Almost all digital single lens reflex cameras have a socket to accept a wired remote.
The purpose of a remote is to trigger the shutter while limiting vibrations, which can be useful for long exposures.
Remotes also allow the shutter to remain open on Bulb mode without holding the shutter button depressed. In Bulb mode you can keep the shutter open as long as desired so you are in complete control of the exposure time.
Wireless remotes are newer and allow the shutter to be activated from a greater distance than using a wired remote.
Many DSLRs have an infrared port in front and at the back of the camera to allow remote operations from almost every angle.