It can be described as an unbroken path along which
an electric current may flow.

A simple circuit consists
of a voltage source, such as battery (Cell, in electricity)
or a generator, whose terminals are connected to those
of a circuit element, such as a resistor, through
which current can flow.

More complex circuits include
additional sources or elements and perhaps Switches,
so interconnected that, when appropriate switches
are closed, each element is included in a closed path
that also contains a source.

Series, parallel, and
non-series-parallel connections are illustrated in
the figure. The effective Resistance of two-series
connected resistors is the sum of the individual resistance.

The effective conductance of two parallel-connected
resistors is the sum of the individual conductances.