Ta is the ninth of the thirty consonants and opens the third line. It writes a voiceless unaspirated stop made with the tip of the tongue at the teeth, further forward than the English t, which is formed on the ridge behind them. In modern Lhasa speech it carries high tone and has fallen together with tha.
Ta is a root letter with no orthographic office of its own, though it takes superscripts readily and takes the ra and wa subscripts.
The line it opens sits at the most conspicuous gap in the whole inherited scheme. In the Indic order from which the Tibetan arrangement descends, the retroflex letters come at exactly this point, between the palatals and the dentals, and in Tibetan they are simply not there. The line runs straight from nya to ta. That absence is a decision, not an oversight: Tibetan has no retroflex consonants and had no use for the five letters that write them. When the language later needed to transcribe Sanskrit accurately, the retroflexes were supplied by a separate device rather than restored to the recitation, so the gap in the alphabet has stayed open for thirteen centuries with the remedy standing outside it.
Because it opens a line, ta also serves the grammars as their specimen dental, in the way that ka serves as their specimen velar. A rule about the dentals is typically stated on ta and then generalised to tha, da and na, which is one more consequence of an alphabet arranged as a grid rather than as a list.