Opposite rays are two rays that share a common endpoint, in this case B, have no other points of intersection, and all points on the two rays are collinear. The important thing to remember about opposite rays is that they share a common endpoint.
I'll attach an image provided of an example of rays that are not opposite.
The two rays I attached in the image provided are not opposite rays even though they do share a common endpoint but all points on the two rays are not collinear.