I believe a reference number is the smallest angle needed to get between any given point on the unit circle and the X axis.
A terminal point, on the other hand, is an actual (x, y) coordinate point that exists on the unit circle.
For example, take pi / 2, or 90 degrees. It has a reference angle of pi / 2, because the smallest angle between it and the x axis is 90 degrees (since it is exactly in the middle of the unit circle with respect to the x axis).
The terminal point at pi / 2 is (0, 1) -- 0 on the x axis, 1 on the y axis.