So for example, here I have our classic y-axis in the vertical direction and x-axis in the horizontal direction. And if I wanted to figure out the slope of this line, I could pick two points, say that point and that point. I could say, okay, from this point to this point, what is my change in x? Well, my change in x would be this distance right over here. Change in x, the Greek letter delta, this triangle here, it's just shorthand for change. So change in x. And I could also calculate the change in y.