Logic gate
Beginner
A tiny circuit that takes one or more on/off signals and produces an on/off answer by a fixed rule.
Novice
A circuit that computes a Boolean function: inputs and output are each 0 (low voltage) or 1 (high voltage). NOT, NAND and NOR are the basic gates in CMOS; AND and OR are built from them.
Expert
A combinational circuit implementing a Boolean function of its inputs. In static CMOS each single-stage gate is a monotone-decreasing (inverting) function; non-inverting functions need a second stage.