Variable Valve Timing, or VVT, is the act of changing the valve timing, or the points at which the cylinder valves in an engine open and close; it may also involve changing the duration, the amount of time a valve is open, and/or the lift, the distance which the valve rises (and thus the speed at which air enters the engine.) Various systems perform some combination of changing timing, duration, or both. VVT systems may also control lift, or the distance the valve travels. Optimally, you would be able to change all of these values arbitrarily over time, as an engine behaves very differently at high RPMs than it does at idle or while cruising. Variable Valve Timing allows you to vary your valve timing to a certain degree, achieving significantly better efficiency at all speeds.
A timing light is a flashing light used to adjust the ignition timing advance on an automobile by means of markings on the crank pulley and on (or near) the engine block. It accomplishes this by flashing a light every time the number 1 spark plug fires. There are two kinds of Timing Light; inline, and inductive. Inline timing lights are connected by unplugging the #1 spark plug wire and plugging a connector inline (hence the name) with that wire. Inductive timing lights have a clip with an inductive sensor built into it, and are simply clipped around the spark plug wire. They will not work with coil on plug ignition, and some of the cheaper and/or older models will not work on distributor-free ("DFI") ignition systems, or some of the lower-power electronically controlled ignition systems. They also do not work on diesel engines.