Mirror line: A line that passes through the centre of a shape with a mirror image on either side of the line

Line of symmetry: it is same as the mirror line

Reflect: mapping of one object from one position to another of equal distance from a given line.

Vertex: A point where two or more-line segments meet.

Perpendicular: Lines that cross at 90 degree

Horizontal: A straight line from left to right (parallel to the x axis)

Vertical: A straight line from top to bottom (parallel to the y axis)