Oscillating motion is motion which moves along a path, then returns along that same path backwards and forwards, backwards and forwards.

In this example the drive wheel is used to power a waving machine, notice how the left to right movement is slower than the right to left. This is because that left to right motion takes place over a longer part of the drive wheels turn.

By moving the drive wheel closer to the pivot point this effect can be exaggerated. The same mechanism is used in mechanical saws to provide a quick return after the cutting stroke.