The **slope** or **gradient** of a line is a number that describes both the direction and the steepness of the line. Given a line represented by `y = mx + b`, it is said that `m` represents its slope. This form of a line's equation is called the slope-intercept form, because `b` can be interpreted as the y-intercept of the line, that is, the y-coordinate where the line intersects the y-axis.

Created with GeoGebra by Vitor Nunes

Change the value of the `m` and `b` parameter to see what happens to the line.

See what happens to the slope of the line when the variable `m` assumes a negative value.

Note that when the value of `m` is zero, the line becomes parallel to the x-axis.

When a line rises from left to right, the slope is a positive number. When a line falls from left to right, the slope is a negative number. The x-axis or any line parallel to the x-axis has a slope of zero. The y-axis or any line parallel to the y-axis has no defined slope.