Tau (capital tiny Τ , τ ), in Greek ταῦ , letter of the Greek alphabet is the nineteenth. In Greek numeration, tau is worth 300.

In Greek old as in Greek modern, tau decides /t/, as in French.

Via the Etruscan Alphabet, it gave the T Latin alphabet.

Use

• In Mathematical,
• the Coefficient of correlation in Statistical;
• the Golden section 1,618… (although the letter Φ is more often used);
• In Physical,
• In Mechanical, a Moment, a force of Rotation;
• In Physical of the particles, the Tauon, an elementary particle;
• lifespan of a process of spontaneous emission;
• In Physical and electronic, a time-constant (for example in a Circuit RC);
• In Chemistry, the Rate of advance of a limited chemical reaction;
• In Astronomy, a measurement of the Opacity of the atmosphere;
• In Biology, it acts of a Protéine implied in the degeneration neuronal E at the time of the Maladie of Alzheimer;
• a old Symbol sometimes represented like a cross. See the article St. Anthony's cross.
• In Heraldic, for the Distinguished soldiers or Virgin S, the tau is used to indicate a unit of the Arme of the transmissions.

In Hebrew alphabet, the letter Tav is written in the form of a T reversed.

• In mathematics, the Tau capital letter reversed is used to represent a perpendicular.