Coordinate Graphs, Lines & Slope
x-axis
The x-axis is the horizontal “floor line” of the coordinate plane — the left-to-right number line. Walking along it, you move sideways but never up or down.
Every point on the x-axis has y-coordinate 0, because being on this line means you have not moved up or down at all. So its points look like (x, 0): for example (4, 0), (-1, 0), and the origin (0, 0). Numbers grow positive to the right of the origin and negative to the left.
When a graph crosses the x-axis, that crossing point is called an x-intercept; these are exactly the points where the height of the graph is zero.
The point (5, 0) lies on the x-axis; the point (5, 1) does not, because its y-coordinate is not 0.
On the x-axis, y is always 0.
See also