There’s some new terminology with Tkinter, defined here for clarity:
A GUI toolkit provided as a library of C routines. This library manages and manipulates the windows and handles the GUI events and user interaction.
The Python Tk interface. A Python module that provides a collection of Python classes and methods for accessing the Tk toolkit from within Python.
The (mostly hidden) language used by Tk and, hence, used by Tkinter to communicate with the Tk toolkit.
A user interface element, such as a text box, combo box, or top-level window. On Windows, the common terminology is control or window.