Collinear points are when you have points that are going to lie on the same line. Let's create a line and put two points on it. Let's put point A on the left side and point B on the right side. If I add another which we can call point C and put that in the middle of our line, we can say that all the points lie on the same line. Points A, B, and C must be collinear in order for B to lie between A and C.