Easting (from latin abscissa, 'cut') is a horizontal coordinate in a rectangular Cartesian plane, which is expressed as the distance between a point and the vertical axis. The x-axis is the horizontal coordinate axis.

The reference system (or mark) about an axis (a straight line), two axes (a plan) or three axes (in space), perpendicular between them and which intersect / cross at a point (known as origin of coordinates) assume the name of Cartesian coordinates.

In a plan, the Cartesian coordinate X is called abscissa, while the Cartesian coordinate receives the name of orderly.

The Cartesian system is thus called to pay tribute to the philosopher, scientist and mathematician René Descartes (1596-1650), who sought to base his philosophical thinking from a point of departure on which rest all the knowledge. Descartes is also considered the creator of analytical geometry.

On the abscissa on an affine right, there is a correspondence between the points of affine right and real (positive if they are to the right of O and negative when they are left). The center of coordinates O corresponds to the value 0.

The system of coordinates in the plane (coordinates Cartesian planar), for its part, is formed by perpendicular lines which intersect at the origin. The position of each of the points of the plane is given by two distances.

Finally, the system of coordinates in space (or three-dimensional Cartesian coordinates) is composed by three perpendicular straight lines between them (X, Y, Z), which intersect at the origin (0) and on which the position of each point of the space can be given by three distances.