What's the difference between a major and minor product?

That's a relative difference; i.e., say the products are 85%A and 15%B then A is the major product and B is the minor product. However, I don't think these numbers are carved in stone. I think if it were 75/25 it is major vs minor or even 60/40 but I think 55/45 would be called essentially "equal" products. I don't believe there is a "rigid" definition of exactly what is major and exactly what is minor.