Learner's definition of CIRCUIT
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
a path or trip around something
— often + of
a legal district that is established within a state or within the federal judicial system
a court of appeals for a particular circuit in the federal judicial system