Tcl is a dynamic interpreted programming language.
Tcl is often used as a scripting engine for applications (which might be written in C), or as an interface to the Tk toolkit.
Tk
Tk is a Tcl package which allows to create and manipulate GUI widgets.
Internally, Tk (as also Ttk) use the functionality of the OS they're running on (i.e. Xlib on Unix, GDI on Windows or Cocoa on macOS).
The Tcl/Tk toolkit can be used from
Python with the
tkinter module.
Ttk
Ttk is a newer family of Tk widgets. Ttk stands for themed Tk.
Python provides bindings to Ttk in the tkinter.ttk module.