What does Τ stand for? 

τ

Tau (uppercase Τ, lowercase τ, or τ {\displaystyle {\boldsymbol {\tau }}} ; Greek: ταυ [taf]) is the 19th 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 or , 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 (

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