Theta (uppercase Θ, lowercase θ or ϑ; Ancient Greek θῆτα ; Modern Greek θήτα ; /ˈθiːtə/, /ˈθeɪtə/) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth . In the system of Greek numerals it has a value of 9.

Read more about Theta:  Greek, Latin, Cyrillic, International Phonetic Alphabet, Symbolism