This is a wiki page for the Linux Documentation Project. I intend to complement the project and update it by adding new words and editing the established words.
I DON'T HOLD ANY COPYRIGHT OR CLAIM ANY. MY WRITINGS AND IDEAS ARE PURELY OPEN SOURCE AND WILL BE AVAILABLE FOR OTHERS FOREVER.
The beginning of the idea was this thread 
But from 2005 to 2012 ..there are many words which are not included such as "Unity" ,"Mate" ,"Desktop", "Window Manager" "Keyring","Cinnamon".
Window Manager formal definition from the Linux Dictionary Project:
A program that controls the display and positioning of graphical windows on a screen; accounts for such variables as screen resolution and user manipulation (for example, a user repositioning or resizing a window).
Desktop formal definition from the Linux Dictionary Project:
Visual component of a graphical user interface upon which icons, programs, and other visual components appear.
as you see these definitions are not easy enough for a beginner and are neither comprehensive nor up-to-date.
My own definition compiled from the internet:
The window manager controls the way your desktop works: how the windows look and act. The window manager decides what kind of decorations to put around the windows. It's the window manager's job to provide ways of controlling the windows, like moving, hiding, resizing, iconifying, or closing them. The window manager decides what window at the moment accepts input from you and what window is on the top. The window manager also controls the ways you do these tasks: what mouse buttons you click or what keys you press in order to accomplish these window management tasks.
Standalone Window Managers:
These window managers can be run without desktop environments.
-Kwin: The KWin window manager is the default window manager for KDE. It is an efficient window manager .
-Metacity: The Metacity window manager is the default window manager for GNOME. It is a simple and efficient window manager.
-DWM: The Dynamic window manager
-MWM: The Motif window manager is a basic, standalone window manager. Since it is designed to be a standalone window manager, it should not be used in conjunction with GNOME or KDE.
-TWB: The minimalist Tab Window Manager, which provides the most basic tool set of any of the window managers and can be used either as a standalone or with a desktop environment. It is installed as part of the X11R6.8 release
-Enlightenment: You want plenty of eye candy but not something as resource-intensive as KDE or GNOME.
-Compiz-Fusion: Can run as standalone windows manager or with a desktop environment.
-Xfwm: Can run as standalone windows manager or with a desktop environment.
These window managers can be run without desktop environments to gain a better sense of their differences. To do this, type the command:
xinit -e <path-to-window-manager>
where <path-to-window-manager> is the location of the window manager binary file. The binary file can be found by typing:
where <window-manager-name> is the name of the window manager you are querying.
As to which Window Manager is best suited for which user? Since there are so many Window Managers I will highlight my favorites:
Afterstep: You want something old-school to give you hours of tinkering fun.
Xfwm: You want a Windows-like interface without the bloatware of GNOME or KDE.The Xfwm (XFWindow Manager) is part of the Xfce Desktop Environment.It is also called xfce window manager.
Compiz-Fusion: This is a full-blown 3 dimensional window manager rife with plugs that do just about everything. If you want something to seriously impress your friends, this is where you want to look.
Fluxbox: You want minimal and fast.
Ever since the inception of GNOME and KDE there has been confusion among new Linux users which is which and which is best to use. The former question is fairly simple to answer. The latter question, however, is a bit more complex due to user-specific needs/wants.
Before we proceed I want to mention some common Linux DE(Desktop Environments):
-Gnome: free, usable, accessible, international, developer-friendly, organized, supported, and a community.
-XFCE: aims to be fast and lightweight, while still being visually appealing and easy to use.
-Mate: a fork of Gnome 2. Mate provides an intuitive and attractive desktop to Linux users.
-Cinnamon: a fork of Gnome 3. Cinnamon strives to provide a traditional user experience.
What is the difference between Window Managers and Desktop Managers ?
With that in mind let us begin by illustrating the differences between a desktop environment and a window manager. We’ll begin by showing how the Linux graphical desktop is layered.
As you can see, in this image , there are basically three layers that can be included in the Linux desktop:
X Windows : This is the foundation that allows for graphic elements to be drawn on the display. X Windows builds the primitive framework that allows moving of windows, interactions with keyboard and mouse, and draws windows. This is required for any graphical desktop.
Window Manager: The Window Manager is the piece of the puzzle that controls the placement and appearance of windows. Window Managers include: Enlightenment, Afterstep, FVWM, Fluxbox, IceWM, etc. Requires X Windows but not a desktop environment.
Desktop Environment: This is where it begins to get a little fuzzy for some. A Desktop Environment includes a Window Manager but builds upon it. The Desktop Environment typically is a far more fully integrated system than a Window Manager. Requires both X Windows and a Window Manager.
Note that a Desktop Environment requires a window manager while SOME window managers doesn't require a Desktop Environment.
A Desktop Environment generally includes a suite of applications that are tightly integrated so that all applications are aware of one another. A Desktop Manager will also include some form of panel that includes a system tray where small widgets can be placed for quick action or information.
Why use a desktop environment over a window manager?
This is a fundamental question. Certainly it depends on the user's preference, but there are some specific questions you can ask yourself to help you decide:
1) Are you new to Linux and open source operating systems in general?
2) Do you prefer a menu-driven style of GUI?
3) Do you like desktop icons?
4) Do you prefer using the mouse to navigate your computer no matter what?
If you answered "yes" to three or more of the questions above, you'll more than likely prefer a Desktop Environment over a standalone Window Manager.
There are two main Desktop Environments: GNOME and KDE. If you are curious as to which is right for you, here is some advice. The latest default GNOME will make users of OS X feel right at home, KDE 3.x will make Windows XP users feel at home, and KDE 4.x will make Windows Vista users feel at home.