Tau

Tau (/ˈtaʊ, ˈtɔː, ˈtɒ/ ^ⓘ; uppercase Τ, lowercase τ or ${\displaystyle {\boldsymbol {\tau }}}$; Greek: ταυ [taf]) is the nineteenth letter of the Greek alphabet, representing the voiceless dental or alveolar plosive IPA: [t]. In the system of Greek numerals, it has a value of 300.

The name in English is pronounced /taʊ/ or /tɔː/, but in Greek it is [taf]. This is because the pronunciation of the combination of Greek letters αυ can have the pronunciation of either [ai], [av] or [af], depending on what follows and if a diaeresis is present on the second vowel (see Greek orthography).

Tau was derived from the Phoenician letter taw (𐤕). Letters that arose from tau include Roman T and Cyrillic Te (Т, т).