From the latest edition of the CRC Handbook of Chemistry and Physics:
The well-known proton, neutron, and electron are now thought to be members of a group that includes other fundamental particles that have been discovered or hypothesized by physicists. These very elemental particles, of which all matter is made, are now thought to belong to one of two families: namely, quarks or leptons. Each of these two families consists of six particles. Also, there are four different force carriers that lead to interactions between particles. The six members or “flavors” of the quark family are called up, charm, top, down, strange, and bottom.