Bollywood = Hindi
Kollywood = Tamil
Tollywood = Telugu
India is a diverse country and every state has its own culture and language so naturally each has their entertainment industries and stars. There are tons of other movie industries in India like Bengali and Marathi films, but they aren't as trashy and commercial as those three big ones so they haven't been stamped with pathetic -wood names.
Hindi films ("Bollywood") are the most popular internationally and nationally probably because the Indian government uses it as the official language so more Indians understand it by default and many non-Indians are most familiar with it too.
There's also a "Nollywood" for Nigerian films.
