Flavor symmetry

Flavor symmetry rotates quark species whose strong interactions are identical. Quark masses break it explicitly, so it is a useful approximate symmetry only among quarks light compared with the hadronic scale.

Isospin is the approximate $SU(2)$ flavor symmetry rotating the up and down quarks. It is accurate because their masses are close and both are small compared with the QCD scale.

The eightfold way organizes light hadrons into approximate $SU(3)$ flavor multiplets built from the up, down, and strange quarks.