1. In animation, the original skeleton from which joint animation is retargeted to the joints of a second skeleton (target). In other words, the source skeleton is the skeleton from which you want to retarget animation data, and the target skeleton is the skeleton to which you want to retarget the source's animation.

2. In rendering, an object that provides illumination to a scene.

3. In MEL, a directive that causes MEL to compile and execute the contents of a script that is stored in a file.