What is a statistical interaction?

A statistical interaction could evolve while considering the relation between 3 or over 3 variables. It states a situation wherein the simultaneous impact of 2 variables on a 3rd is not considered to be additive. Is it within regression analyses that the interactions are usually being considered. An interaction would not generally imply that the direction with regard to an effect is varied at various levels of a variable. There would be interaction till the extent of an effect when being compared to another would be higher at one of the levels of a variable.