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; from which one is to determine a particular quantity.
3.nounA small correction to observed values to remove the effects of systematic errors in an observation.