tau; Τ, τ +

(Greek: the nineteenth letter of the Greek alphabet; Τ, τ)

1. The 19th letter of the Greek alphabet (T, τ) equivalent to the English t.
2. As a numeral, it denotes 300.
tau protein
A protein associated with the assembly, stability, or enhancement of the polymerization of microtubules.

You can see all of the letters of the Greek Alphabet on this page.