Motivated light is an artificial light source that creates an effect that is seen within the frame, but which is understood and believed by the audience to be caused or 'motivated' by an unseen or indeed visible 'real world' light source (and not the technical light source used by the lighting director or cinematographer)

the justification given in film for the presence of an element

a number of images printed over each other.

a number of images printed beside each other within the same frame, often showing different camera angles of same action, or separate actions. Also called split screen