Compositing is the combining of visual elements from seprate sources into single Image often to create the illusion that all those elements are parts of the same scene.
Chroma keying is a technique fro compositing (layering) two images or video streams together based on color hues (Chroma Range).
Wire removal is a visual effects technique used to remove wires, cables in films, usually used as a safety precaution or to simulate flying actors or miniatures.
Crowd multiplication is the process of simulating the movement of a large number of entities or charachters in a given scene
The term rotoscoping refers to the technique of manually creating a mette for an element on a live -action plate so it may be composited over another background.