# Abscissa

In mathematics, an **abscissa** (plural **abscissae** or **abscissæ** or **abscissas**) is the perpendicular distance of a point from the y - axis. Usually this is 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 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 (-1.5, -2.5), -1.5 is called the abscissa and -2.5, the ordinate.

## See also

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- Ordinate
- Dependent and independent variables
- Function (mathematics)
- Relation (mathematics)
- Line chart

## References

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

## External links

de:Kartesisches Koordinatensystem#Das Koordinatensystem im zweidimensionalen Raum