If you are asked to reflect a shape in the x-axis then the x-axis is acting as the mirror line. Also if you are asked to reflect a shape in the y -- axis the
How to Reflect a Shape Across the x-axis
Reflections in Geometry - Miss Kuiper's Classroom
How Do You Use Coordinates to Reflect a Figure Over the X-Axis?
Reflecting shapes (article), Reflections
Reflections
Lesson Explainer: Reflections on the Coordinate Plane
Examples on how to reflect a shape in the x-axis or y-axis on a coordinate grid. - HubPages
Solved 2. a. Draw the result of reflecting the shaded shapes
Reflecting a Shape in the Y-Axis Using Cartesian Coordinates (Key Stage 3)