**Axis:** A fixed reference line for the measurement of coordinates. The variable considered a cause is placed on the horizontal axis, and the variable that is considered an effect is placed on the vertical axis.

**Coordinates:** Each of a group of numbers used to indicate the position of a point, line, or plane.

**Coordinate Plane:** The **plane** determined by a horizontal number line, called the x-axis, and a vertical number line, called the y-axis, intersecting at a point called the origin. Each point in the **coordinate plane** can be specified by an ordered pair of numbers.

**Distance Formula:**** **The **distance formula** is used to determine the **distance**, d, between two points. If the coordinates of the two points are (x_{1}, y_{1}) and (x_{2}, y_{2}), the **distance** equals the square root of x_{2} − x_{1} squared + y_{2} − y_{1} squared.

**Graph:** a diagram showing the relation between variable quantities, typically of two variables, each measured along one of a pair of axes at right angles.

**Midpoint Formula:** The point halfway between the endpoints of a line segment is called the **midpoint**. A **midpoint** divides a line segment into two equal segments. By **definition**, a **midpoint** of a line segment is the point on that line segment that divides the segment two congruent segments.

**Point:** A precise location or place on a plane. Usually represented by a dot.