TWM, The Window Manager
I may be missing the sarcasm but encase "what is a window manager" was an honest question:
TWM is a basic window manager. It does little more than display a background and provide a way to interact with windowed programs. It is the absolute minimum one needs to layer over the graphic engine to work with GUI programs. It's named literally; The Window Manager (TWM). This is like naming a word processing program "Word Processor".
X.org (formerly Xfree86) is a graphic engine. Without a window manager of some form or desktop environment (which includes a window manager component) you'll get nothing more than a blank screen and whatever program you may have specified to open; no window border, no title bar and buttons but you can interact with the program's own GUI elements.
Imagine separating IE (the windows window manager and widget set) from the graphics engine it sits on top of. Same graphics engine back end provided by Windows but easily interchangeable layer on top to manage the display and interaction with the windowed applications.
On the window manager/desktop environment side, there is at least twenty if not more choices available focusing on various user needs. On the graphic engine side, there is X.org which sits squished inbetween the graphics you see and click on and the text environment providing the base userland on top of the kernel.
