The slope of a line can positive, negative, zero or undefined.
Undefined slope-When the line is exactly vertical, it does not have a defined slope. The two x coordinates are the same, so the difference is zero.
Zero slope- The line is exactly horizontal. The slope of any horizontal line is always zero. so its slope is zero.
Negative slope- The line slopes downwards to the right so the slope will be a negative number.
Positive slope- The line slopes upwards to the right so the slope will be a positive number.