I keep coming across the terms "voltage sink" and "current sink" but can find no satisfactory definitions. Can anyone tell me what these terms refer to and how their effects are used?
To sink is to go down. The output of a circuit sinks if it pulls down to ground. It sources if it goes up to a higher voltage.
Digital logic outputs sink down to ground and source up to the positive supply if it is Cmos with a high load resistance.
You can also have a Constant Current Sink which is a regulated current pulling to ground, and a Constant Current Source which is a regulated current pulling high.