Abscissa

the term given to the horizontal or x-co-ordinate when describing the position of a point on a graph. It is the distance of the point from the vertical or y-axis. For example, a point two units along the x-axis and three units up the y-axis is said to have CARTESIAN CO-ORDINATES (2,3) where the abscissa is 2.

Taken from Dictionary of Science

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In mathematics, abscissa (plural abscissae) refers to the first element of an ordered pair.

It is the first of the two terms (x, y) by which a point is referred to, in a system of fixed rectilinear coordinate (Cartesian coordinate) axes. The abscissa is also known as the "x" coordinate of a point. The second coordinate, or "y" coordinate, is called the ordinate.

Taken from Wikipedia

X-Axis

the "horizontal" axis when constructing and plotting a graph.

Taken from Dictionary of Science

The coordinate surfaces of the Cartesian coordinates (x, y, z). The z-axis is vertical and the x-axis is highlighted in green. Thus, the red plane shows the points with x=1, the blue plane shows the points with z=1, and the yellow plane shows the points with y=-1. The three surfaces intersect at the point P (shown as a black sphere) with the Cartesian coordinates (1, -1, 1).

Taken from Wikipedia