**Transformation** - A rule that assigns to each point of a figure another point in the plane called its image. Examples: Reflection, Translation, Rotation, and Dilation.

**Isometry **- A transformation that preserves size and shape. The image of a figure under an isometry is congruent to the original figure. Also called a rigid transformation. Examples: Reflection, Translation, and Rotation.

**Symmetry** - The property that a figure coincides (matches) with itself under an isometry.

**Reflection** - An isometry in which every point and its image are on opposite sides and the same distance from a fixed line.

**Reflectional Symmetry** - The property that a figure coincides (matches) with itself under a reflection. Also called line symmetry or mirror symmetry.

**Rotation** - An isometry in which each point is moved by the same angle measure in the same direction along a circular path about a fixed point. Rotation means turning.