Who is asking: Student
You should use a dictionary to find a definition of the word symmetry.
A geometric figures in the plane can have symmerty in a line or symmetry in a point.
Two points in the plane are symmetric in the line of symmetry L if the two points are the same distance from L and the line joining them is perpendicular to L.
Two points in the plane are symmetric in a point P if the midpoint of the line joining the points.