Definition: The principal or horizontal axis in a graph along which the coordinates all have the value of zero in relation to all other coordinates.

Etymology: The x-axis comes from the system of coordinates we use today called the Cartesian system. Mathematician René Descartes developed this graphing system, and the earliest known use of the term is dated to 1886. The legend states that Descartes was lying in bed one morning watching a fly on the ceiling and pondered how best to describe its location. He decided that using one of the corners as his point of reference was the best way to begin.

From there, all that was needed would be to measure how far the fly was from the horizontal edge, how far it was from the vertical edge, and taking those two numbers; he could quantify the exact location of the fly using those coordinates no matter where the fly ended up.

In a Sentence

The x-axis is always stated first.

The horizontal line that represents zero in a graph is known as the x-axis.

The point where the lines from the x-axis and the y-axis meet are the solution.