A
key frame in
animation and
filmmaking is a drawing that defines the starting and ending points of any
smooth transition. The drawings are called
"frames" because their position in time is measured in
frames on a strip of
film. A sequence of key frames defines which movement the viewer will see, whereas the position of the key frames on the film, video, or animation defines the
timing of the movement. Because only two or three key frames over the span of a second do not create the illusion of movement, the remaining frames are filled with
inbetweens.