I'm a foregner, can someone explain to me what is the VSP?

I've been reading here about some changes and that lenses are devided into categories and things like that and I am confused.
1) what is the VSP?
2) What is the catogories and what do they mean?
3) why are some looking for lenses that are not on the vsp?

Thanks a lot!

I'm a foregner, can someone explain to me what is the VSP?