It may be added that if V is the potential difference across a two
terminal device (in a DC circuit) and I is the current "flowing" into
and out of that device, then the device is a site of energy
transformation - either a sink or a source, with respect to the circuit:
1) If I is flowing down the potential hill, V, the device is a sink and
is sinking energy at the rate P=VI;
2) If I is flowing up the potential hill, V, the device is a source and
is "giving" energy to the circuit at the rate P=VI.