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 (x1, y1) and (x2, y2), the distance equals the square root of x2 − x1 squared + y2 − y1 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.