This particle can not be described, for the Tau that can be spoken of is not the true Tau.
Tau = a small, diminutive, and little alien species from the game of Warhammer 40k. When you get a box of tau, it costs over 100 dollars for a little 10 x 10 cm tank, either way, you get these little models, you put them together, paint them (With great difficulty) and then find other nerds with similar little human-like models and then use tape measures ect and pretend to whip each others ass, people spend thousands upon playing a glorified version of chess.
Tau are currently living in the Japanese version of the WH40k world. They fool people into thinking they're Small, Smart, Hardworking, Funny Looking and have lots of electronic dealies to kill each other with but are really just slighly overdeveloped foetus. They're fanatical but hide it under the guise of serving one tau who acctually has a penis, played with verve by George Hamilton. Tau collectors are easily defeated by a Megaton 10,000 hyperdense laser cannon, AKA shotgun painted blue
Tau are best known for their invlovment in the Quantum Relativity War's greatest battles such as Einstien v. Planque, and Godzilla v. Virtual Super Monkey Godzilla.
More recently they have been known to have started hostilities with thier electron ancestors, known as the Electrofunts.