Also known as: Clade
A subgroup of genetically related HIV-1 viruses. HIV-1 can be classified into four groups: M Group, N Group, O Group, and P Group. Viruses within each group can then be further classified by subtype. For example, the HIV-1 M group includes at least nine subtypes: A1, A2, B, C, D, F1, F2, G, H, J, and K.