In geometry, horizontal refers to something that is parallel to the horizon or perpendicular to vertical lines. In terms of graphs, it means having zero slope or being flat along the x-axis.
Related terms
Vertical Line: A line that runs straight up and down (perpendicular) with respect to the x-axis.
Slope Intercept Form: An equation representing a linear function where y = mx + b, where m represents slope and b represents y-intercept.
Gradient: The rate at which something changes as you move horizontally across its domain; often used interchangeably with slope in calculus.