1.n. the state of a system on which excessive demands are made. Examples include muscular strain (excessive tension in a muscle usually due to an activity overload) and psychological strain, usually due to an emotional overload. 2.n. a specific group within a species whose members possess a common distinguishing characteristic. 3.n. excessive effort or exertion. 4.vb. to distort, alter, or injure as a result of such excess or the application of external force. 5.vb. to filter.