Axis of Symmetry
A line of symmetry for a graph. The two sides of a graph on either side of the axis of symmetry look like mirror images of each other.
This is a graph of the parabola y = x2 – 4x + 2 together with its axis of symmetry x = 2.
The axis of symmetry is the red vertical line.
See also
Point of symmetry, axis of symmetry of a parabola, symmetric about the x-axis, symmetric about the y-axis