I saw this repository. sublimehq/Packages I use sublime text 3, but I don't know tmLanguage file. Also I googled definition of it, but I couldn't find it. What is it?
tm stands for TextMate. It's a text editor for Mac OS X only and was revolutionary in its time since most of its features are pushed to extension packages instead of residing in the main program.
Sublime Text carried on the idea and made it cross platform. Sublime was designed to be compatible with TextMate extension packages.