Reflection over the y-axis
A reflection is a type of Rigid Motion. On a coordinate plane, a reflection is depicted by the movement of coordinates over a line of reflection. Without the coordinate grid present we can tell that a reflection is precise because each image and it's corresponding pre-image is equidistant from the line of reflection and is across the line at a 90 degree angle, and therefore perpendicular to the line.

Information: Reflections