Well a good starting point might be the tutorial I wrote here on choosing stepper motors...

A glossary is a good idea... let me think on it... but for a simple explanation:

most CNC machines use some form of screw mechanism to convert rotary motors to linear motion. The motor turns the screw and a nut riding on the screw transfers the power to the linearly moving part. Screws are generally made of carbon steel. To maximise power transmission they have special thread forms, usually trapezoidal or square (Acme). Minimising friction is critical, so the nuts are made of bronze or of hard but machinable engineering plastics like delrin. Typically the energy transmission of such an arrangement is 30% because of the frictional losses. Nuts are not perfect, if there was a 100% fit the friction would be very high, so there is a point where the screw turns but the slop between the thread of the screw and that in the nut means the nut doesnt move.. it is tiny but measurable. This is backlash and its one of the high goals of engineering to minimise it but still make the screw turn freely. Ballscrews use a different thread form and the nut comprises a number of ball bearings that run round the screw thread and recirculte back through a tube. Because the balls rotate and therefore have low friction they can be a much closer/tighter fit than a conventional nut, meaning reduced backlash (not zero as some claim) and higher efficiency (80%). Ballscrews are the screw of choice but the cost is 20 - 50x a standard screw.