The letter ת represents the phoneme /t/. In Modern Israeli Hebrew, this phoneme is pronounced [t].
In the Masoretic Text, the letter ת takes a dagesh (תּ) not only when geminated, but also at the start of a word or after a consonant. In Ashkenazi Hebrew, it is pronounced [t] when it has a dagesh, and [s] in other cases. In Yemenite Hebrew, it is pronounced [t] when it has a dagesh, and [θ] in other cases; it is commonly believed that the same was true in Classical Hebrew.
Nouns ending in ת tend to be feminine, and many adjectives and participles form their feminine singular forms by appending ת to the masculine singular form (plus vowel changes). This is a reflex of Proto-Afroasiatic.
In many cases ת alternates with silent ה in different forms of a verb or noun; for example, feminine nouns whose singular indefinite forms end in ה tend to have singular construct forms ending in ת. (In many cases, this results from an original etymological /t/ having been lost in certain word-final contexts.)
