Hypercharge is one of two quantum numbers of the SU(3) model of hadrons, alongside isospin I3.
The SU(2) model has multiplets characterized by a quantum number J, which is the total angular momentum.
Each multiplet consists of 2J + 1 substates with equally-spaced values of Jz, forming a symmetric arrangement seen in atomic spectra and isospin.
With the advent of the quark model, it is now obvious that strong hypercharge, Y, is the following combination of the numbers of up (nu), down (nd), strange (ns), charm (nc), top (nt) and bottom (nb): In modern descriptions of hadron interaction, it has become more obvious to draw Feynman diagrams that trace through the individual constituent quarks (which are conserved) composing the interacting baryons and mesons, rather than bothering to count strong hypercharge quantum numbers.
Weak hypercharge, however, remains an essential part of understanding the electroweak interaction.