1.NounThe act or process of equating two or more things, or the state of those things being equal (that is, identical).
"We need to bring the balance of power into equation"
2.NounAn assertion that two expressions are equal, expressed by writing the two expressions separated by an equal sign; in mathematical problems, equations describe various essential aspects of the problem, each of which contributes to the resolution of the problem in part.
3.NounA small correction to observed values to remove the effects of systematic errors in an observation.