Horizontal line is a line which is parallel to X-axis on Cartesian coordinate system. Horizontal line goes from left to right or right to left. Since all the points on horizontal line are equidistant from X-axis, each point on it has the same y coordinate.

Every point on a horizontal line is equidistant from X-axis. Equation of a horizontal line is the same as that of the line parallel to X-axis. Equation of the horizontal line is given below:
Horizontal Line
Where, b is the intercept of y. "b" is a positive quantity, if horizontal line lies above X-axis. While "b" is a negative quantity, if horizontal line lies below X-axis.