Imagine a disc-shaped lollipop with a horzontal slot in it.
A crankshaft passes through this slot.
The lollipop stick is constrained in a tube or similar, so that it can only move up and down (i.e. along the axis of the stick).
As the crank rotates, it raises and lowers the lollipop.
So it’s a cam, of sorts, but the follower encloses the cam.
Does this construction have a name?