n. 1. a circular motion of a configuration about a given point or line (the axis) without a change in shape; a rigid motion leaving fixed the given point or line. It is a transformation resulting from turning the entire plane about a fixed point in the plane; this is effected by a change of variables of the form
x' = xcos θ + ysin θ,
y' = -xsin θ + ycos θ.
The positive direction is taken to be anti-clockwise. 2. (Euclidean geometry) a transformation in which the coordinate axes are turned about the origin. 3. (abbrev. rot) (Vector analysis) another name for curl. See also irrotational.