# Abscissa

Illustration of a Cartesian coordinate plane. The first value in each ordered pair is the abscissa of the corresponding point.

In mathematics, abscissa (plural abscissae or abscissæ or abscissas) most often refers to the horizontal coordinate of a point in a two-dimensional rectangular Cartesian coordinate system. The term can also refer to the horizontal axis (typically x-axis) of a two-dimensional graph (because that axis is used to define and measure the horizontal coordinates of points in the space). An ordered pair consists of two terms—the abscissa (horizontal, usually x) and the ordinate (vertical, usually y)—which define the location of a point in two-dimensional rectangular space.

In a simple definition, abscissa is the perpendicular distance of a point from the y - axis.

$(\overbrace{x}^\text{abscissa}, \overbrace{y}^\text{ordinate})$

## In parametric equations

In a somewhat obsolete variant usage, the abscissa of a point may also refer to any number that describes the point's location along some path, e.g. the parameter of a parametric equation.[1] Used in this way, the abscissa can be thought of as a coordinate-geometry analog to the independent variable in a mathematical model or experiment (with any ordinates filling a role analogous to dependent variables).

## Examples

• For the point (2, 3), 2 is called the abscissa and 3, the ordinate.
• For the point (5, 15), 5 is called the abscissa and 15, the ordinate.