What does T IS mean in Community?

It is

English auxiliary verbs are a small set of English verbs, which include the English modal verbs and a few others. Although definitions vary, as generally conceived an auxiliary lacks inherent semantic meaning but instead modifies the meaning of another verb it accompanies. In English, verb forms are often classed as auxiliary on the basis of certain grammatical properties, particularly as regards their syntax. They also participate in subject–auxiliary inversion and negation by the simple addition of not after them.

see more »