A map between metric spaces that preserves distances exactly: for all points x and y, the distance between f(x) and f(y) equals the distance between x and y.
A map between metric spaces that preserves distances exactly: for all x,y, d(f(x),f(y)) = d(x,y). In Euclidean spaces isometries are geometry-preserving transformations such as translations, rotations, and reflections.