In telecommunication, the term circuit has the following meanings:

1. The complete path between two terminals over which one-way or two-way communications may be provided.
2. An electronic path between two or more points, capable of providing a number of channels.
3. A number of conductors connected together for the purpose of carrying an electrical current.
4. An electronic closed-loop path among two or more points used for signal transfer.
5. A number of electrical components, such as resistors, inductances, capacitors, transistors, and power sources connected together in one or more closed loops.

Source: from Federal Standard 1037C and from MIL-STD-188

In sport, the circuit means a closed, quite often circular racing track. Typical examples include various motor sports, cycling, running, skating etc.

Circuit is a political administrative division.