What is a digital camera lens adapter?

It is a lens that mounts on the end of your camera lens. Some are wide angle adaptors (0.75x is an example) and some are multipliers (1.5x or 2x) which move you half the distance to the subject you are shooting. They can be handy adaptors, but can also reduce critical focus in your pictures, or degrade sharp focus. There are also lens adaptors for digital SLR cameras to use lenses from another type of camera. A lens adaptor could also screw onto the end of a lens to allow filters of another size to be mounted in front of the lens. ----

Just an added note: Although the principle is the same, not all adapters mount on the end of the camera lens. Some adapters mount to threads on the body which may be hidden by a removable ring. So the camera may not always appear to have threads when it does, if you know where to look. Check the manual.