Definition of electromotive force (e.m.f)

i) The work done by a source in driving a unit charge around a complete circuit.
ii) a measurement of the rate at which energy ( joule) is transferred per electric charge (coulomb) from an energy source such as a battery or a dynamo, in the kinetic energy of the moving charge.

e.m.f = Electric energy provided by the source Charge that flow from the source

The unit of e.m.f is JC-1 or volt, V.
1 V = 1JC-1