flavor
/ FLAY-ver /
In particle physics, 'flavor' is just a quirky name for the kind, or type, of a quark or lepton. It has nothing to do with taste — it is a label, the way 'spades, hearts, clubs, diamonds' label the suits of a deck. Asking what flavor a quark has is like asking which of the six kinds it is.
There are six quark flavors (up, down, charm, strange, top, bottom) and six lepton flavors (electron, muon, tau, and their three neutrinos). Flavor is what distinguishes, say, an up quark from a charm quark even though they share the same electric charge and spin — the difference is essentially their mass and which generation they belong to. Most forces leave flavor untouched: electromagnetism and the strong force never turn one flavor into another. The weak force is the special exception — it can change a quark's flavor, which is exactly what happens when a neutron turns into a proton in radioactive beta decay (a down quark becomes an up quark).
Flavor matters because flavor-changing processes are the heartbeat of the weak force, and the precise rules of how flavors mix and change carry some of the deepest information in the model. The pattern of quark mixing, and the related mixing of neutrino flavors, is where physicists look for tiny differences between matter and antimatter — clues to why the universe is made of matter at all.
In beta decay a neutron becomes a proton because one of its down quarks changes flavor into an up quark — a flavor change only the weak force can make happen.
Only the weak force can change a particle's flavor.
Despite the appetizing name, flavor has nothing to do with taste or any physical property you could sense — it is purely a label for which type of quark or lepton you are dealing with.