Preset time delay (2, 5 or 10 seconds) before the shutter fires. Allows the photographer to get into the picture without using a cable release or remote control. It is also great for taking macro shots as you don't touch the camera to trip the shutter and thus eliminates any camera shake.
The self timer allows the camera to take a picture unattended. With it you can take a picture of yourself. Once the timer is set, you usually have about ten seconds to get into the picture. A flashing light or a tone signals when the picture is about to be taken.
Mechanism that delays the shutter action after being actioned. Useful both to allow for the photographer to be included in the image and as means to reduce camera shake from shutter button jerking.
A Self timer is a device on a camera that, when enabled, gives a delay between the pressing of the shutter release and the shutter firing. It is most commonly used to allow photographers to take a photo of themselves, hence the name.