Horizontal axis

The "left-right" or "west-east" axis on a graph or grid.

Vertical axis

The "up-down" or "north-south" axis on a graph or grid.

Direct relationship

The relationship between two variables which change in the same direction for example product price and quantity supplied.

Inverse relationship

The relationship between two variables which change in opposite directions for example product price and quantity demanded.

Independent variable

The variable causing a change in some other (dependent) variable.

Dependent variable

A variable which changes as a consequence of a change in some other (independent) variable; the "effect" or outcome.

Slope of a line

The ratio of the vertical change (the rise or fall) to the horizontal change (the run) between any two points on a line. The slope of an upward sloping line is positive reflecting a direct relationship between two variables; the slope of a downward sloping line is negative reflecting an inverse relationship between two variables.

Vertical intercept