1, Zero Point: A base point for the machine to measure it's tool position from. A limit switch could simply tell the software it had better stop now because what comes next ain't gonna work :D

2, Transition: The switch closes or the switch opens. A logic gate switches low-high or high-low.

3, Hysteresis: The difference, distance-wise, or volt-wise between the transitions

4, Opto Slot: An electronic gizmo that tries to shine a beam of light across a small gap and tells you when it can't do it because something is in the way.

5, Logic Gates: TTL, CMOS, AND's, OR's, NAND's, NOR's, XOR's, inverters, flops etc.