A group of transistors, resistors and capacitors that perform a particular electronic function. Circuits may be made of discrete components wired together or be built into a chip. For example, a chip may contain a single circuit, such as a video codec, or an entire subsystem with many circuits, such as a CPU.
Circuits Are Hardware
Circuits are always hardware; however, a "software circuit" may refer to a circuit designed in the computer and simulated before being physically manufactured. See discrete component