Which of the following describes an isometry?

An isometry is a transformation that preserves distance, meaning that the lengths of line segments remain unchanged before and after the transformation. This can include various types of movements such as translations (sliding), rotations (turning), and reflections (flipping) that do not affect the size or shape of the geometric figures involved.

Because an isometry maintains the original distances between points, it ensures that the figure retains its proportions and overall appearance. This characteristic makes isometries crucial in understanding congruence in geometry, as two shapes are congruent when one can be transformed into the other through isometries without any changes to size or shape.

The other options do not accurately describe the properties of isometries: they do not change the shape or affect area, nor do they alter the orientation in a way that typically defines isometric transformations.