When discussing engines, the ratio of output work to input work expressed as a percentage is called

Efficiency η is the ratio of input work over the output work. It is defined as:

η=work done/heat absorbed = (Q₂-Q₁) / Q₁ where Q₁ is the heat absorbed and Q₂-Q₁ is the work done. This ratio is never greater or equal to 1, or 100% because the second law of thermodynamics doesn't allow it.