A generation is a set of one of each charge of quark and lepton. Each generation is heavier than the previous one.

All visible matter in the universe is made from:
     up and down quarks,
     and electrons,
which are all in the first generation.

Although second and third generation particles are unstable and quickly decay into first generation particles, they have an important impact on our natural world. Physicists can also make them in collision experiments in order to study them in a more controlled setting.

We thank Fermi National Laboratory for the use of their "Generations of Matter" image.