1 [countable]HM a statement in mathematics that shows that two amounts or totals are equal :

In the equation 2x + 1 = 7, what is x?

2 [countable usually singular] the set of different facts, ideas, or people that all affect a situation and must be considered together :

3 [singular] when you consider that two things are similar or connected :

the equation of violence with power

Definition from the Longman Dictionary of Contemporary English

Advanced Learner's Dictionary.

Advanced Learner's Dictionary.