What is an
A circuit is a
structure that directs and controls electric currents, presumably to
perform some useful function. The very name "circuit" implies that the
structure is closed, something like a loop.
That is all very well, but
this answer immediately raises a new question: "What is an electric
current?" Again, the name "current" indicates that it refers to some
type of flow, and in this case we mean a flow of electric charge, which
is usually just called charge because electric charge is really the only
kind there is.