1 : a series of performances, sports events, lectures, etc., that are held or done at many different places — usually singular • She will be on a lecture circuit [=she will be traveling from place to place giving lectures] promoting her new book. • He is one of the most popular drivers on the (racing) circuit. • the women's tennis circuit
2 : a path or trip around something • It takes a year for the Earth to make one circuit around the sun. — often followed by of • She made a circuit of the museum.
3 : the complete path that an electric current travels along • electric/electronic circuits • a 120-volt circuit
4 a US, law; or Circuit : a legal district that is established within a state or within the federal judicial system • She was appointed chief judge for the circuit. • The case will be heard by a court in the Third Circuit.
4 b US, law Circuit : a court of appeals for a particular circuit in the federal judicial system • The Second Circuit ruled today against the plaintiff.