Smear frames
Also said as Smear, Motion smear, Multiples
One or two distorted drawings, shown so briefly you never quite see them, that stretch an object along its path during a very fast move. It is the hand-drawn version of motion blur.
A very fast move in crisp frames looks like a teleport, because the eye sees no link between the poses. A smear bridges them in a single frame, and you feel the speed.
Say it
“The sword swing looks like it teleports. Add one smear frame between wind-up and contact: a crescent along the blade's path, held for a single frame at 24.”
Where you’ve seen it
Chuck Jones's The Dover Boys at Pimento University (1942) is the classic early example. In games, Hollow Knight's nail swings use them, as sword attacks often do.
Not to be confused with motion blur
Motion blur is calculated by the renderer and softens everything. A smear is drawn, on purpose, and can bend, stretch and be as stylish as any other pose.