QT can refer to several things. There's the QT widget set made by Troll Tech and used in KDE. That used to be evil and not free so to GNU purists it was the devil. Since then the X11 libraries for it went GPL in version 2.2. I'm still critical of it, though, because it still sucks, still uses heavily preprocessed C++, and still isn't free for non-X11 platforms like Win32 or framebuffer. QT is also a common abbreviation for QuickTime among Mac buffs.

This is also used by idiot AOL-using teenage girls to mean "cutie".