n. The act of turning or the state of being turned aside from a straight line or course; a turning from a true line or the regular course; deviation.n. Figuratively, deviation from the right, regular, or expected course of action or thought; aberration.n. Specifically Nautical, the deviation of a ship from her true course in sailing.n. In optics, a deviation of the rays of light toward the surface of an opaque body; inflection. See diffraction.n. In electricity, the deviation or swing of a magnetic needle from the zero of its position: often measured in degrees.n. In mathematics: The distance by which a curve departs from another curve, or from a straight line.n. Any effect either of curvature or of discontinuous change of direction.n. In mech., the bending of material under a transverse strain, as of a beam under the weight of a load.n. In entomology: The state of being bent downward: as, a deflection of the side of the pronotum.n. A deflected part or margin.