What does gtk mean in text slang?

"GTK" is not a common text slang abbreviation. It's most likely an abbreviation for the Gnome ToolKit, a cross-platform toolkit for creating graphical user interfaces.

If you encountered "GTK" in a text message or online, it's possible the sender was referencing something related to software development or user interface design.

If you can provide more context, I might be able to give you a more accurate answer.