Undercrank: This term is used to describe the technique of filming something at a lower frame rate than would normally be used (e.g., 24 frames per second in film) in order to make it (when played back at the normal 24 fps) appear to be moving faster. This technique was used in the Raiders of the Lost Ark sequence where Indy slides under the truck and then is dragged along behind. The truck moved at a slower speed in real-life than it appeared to. I think some stunts in various Roy Rogers films used this technique to safely get a character onto a moving vehicle.

Overcrank: The opposite of the above.

Just when film cameras were coming out, there was a crank on the side of the camera. Camera operators would hand-crank it in order to record anything, and if they cranked it slower than normal, you get the term “undercrank” and it’s definition. Same with “Overcrank.”