The "slope" of a line is the number which tells us how much the line tilts. In order to find the slope of a line, identify two points through which the line passes. To find the slope of the line, we simply find the difference of thte y-coordinates, and we divide this difference by the difference of the x-coordinates. The concept of the slope is typically denoted by the letter m. Lines with horizontal slopes have a slope of "0," lines with positive slopes gradually rise to the right, and lines with negative slopes gradually move downward.
The steeper the rise of a line, the more positive the slope is, whereas the opposite is true of a line with a negative slope. Vertical lines of the sort we discussed before, written x = [insert value] have no slope whatsoever. Keep in mind that we would not say of such vertical lines that their slope is 0. We say, rather, that their slope is "undefined." An undefined expression is "An expression in mathematics which does not have meaning and so which is not assigned an interpretation. For example, division by zero is undefined in the field of real numbers."