The slope 1/2 means that if you start at any point on the line and go to the right two and up one, you will hit the line again. That means the there are an infinite number of parallel lines that can have 1/2 as their slope. Each one has a formula (y=mx+b is the general slope-intercept formula, with b being the height at which that line crosses the y axis) using 1/2 as its m, and the b changes to show the y-intercept for that particular line. As an example, y=1/2x+2 is a line with the slope we described and it crosses the y axis at (0,2). Raise the value of b and the line moves to the right (and keeps the same slope, or lean). Reduce the value of b, and it slides to the left.