What does a visa R class BBBCC mean? What type should I put for deferred action?

I always thought I had entered the US with a B2 - visitor's visa but now I'm not sure. On my Meixcan visa it says visa/type R class BBBCC. The internet has given me conflicting information. Some websites say the R stands for regular and other for religious which doesn't seem like it would apply to me. I also read that BBBCC is some special visitor's visa for Mexico.