# Glossary for Lesson 5-1: Coordinates

### Coordinate Plane

A coordinate plane, or the Cartesian coordinate plane, is made up of one horizontal number line, called the horizontal axis, and one vertical number line, called the vertical axis. Each axis represents a different variable.  By convention, the variable x is usually shown on the horizontal axis, and the variable y is usually shown on the vertical axis.  Every point on the plane containing these axes can be defined by a number indicating its horizontal position and a number indicating its vertical position.  These numbers, called the point’s coordinates are normally written with ordered pair notation.  If a point has a horizontal coordinate of 3 and a vertical coordinate of -4 , it can be identified by the ordered pair (3,-4)

### The Origin

The origin is the point on a coordinate plane where the axes meet one another, giving it the coordinates (0,0).

### x-Axis

The x-axis is the horizontal number line the Cartesian coordinate plane.  It represents values that the variable x in an equation might equal.  The origin represents an x-value of 0 , positive values lie to the right, and negative values lie to the left.

### y-Axis

The y-axis is the horizontal number line the Cartesian coordinate plane.  It represents values that the variable y in an equation might equal.  The origin represents a y-value of 0, and values increase going up the axis and decrease moving down.