Analog

Analog is a term used in computer-related discussions to describe the lowest conceptual level at which computer circuits can be examined. (Obviously, in actuality, all computers are 'analog' at their lowest level, since they are built out of electrical circuits.)

As such, things such as voltages, resistors and transistors are the concepts used. Note particulary that voltages are not binary, but can take any value (one of the meanings of 'analog'); this is important in topics such as meta-stability.