anaconda – confused about the pytorch cuda version

I am somehow new in the coding Pytorch and CudaSo I prepared a good environment with Anaconda and tried out a few things from a few tutorials.

The point is, I'm still confused about the concept of the Cuda version that comes with it Pytorch Package like (eg Pytorch Cuda90) which points to cuda 9.0.

My question is, what does this number refer to? Is it the release of the GPU? because if I walk for example nvcc --version Command shows me that I have

Cuda Compilation Tools, Version 10.0

but what I installed in Anaconda was pytorch cuda90 and it works! although I'm not sure why I chose that?

Could someone please clarify?