Enlightenment is not just a window manager for Linux/X11 and others, but also a whole suite of libraries to help you create beautiful user interfaces with much less work than doing it the old fashioned way and fighting with traditional toolkits, not to mention a traditional window manager. It covers uses from small mobile devices like phones all the way to powerful multi-core desktops (which are the primary development environment).
Enlightenment is the flagship and original name bearer for this project. Once it was just a humble window manager for X11 that wanted to do things differently. To do them better, but it has expanded. This can be confusing so when we refer to Enlightenment, we may mean the project as a whole or just the window manager proper. The libraries behind Enlightenment are referred to as EFL collectively, each with a specific name and purpose.
The window manager is a lean, fast, modular and very extensible window manager for X11 and Linux. It is classed as a "desktop shell" providing the things you need to operate your desktop (or laptop), but is not a whole application suite. This covered launching applications, managing their windows and doing other system tasks like suspending, reboots, managing files etc.
(Text from enlightenment.org, image from wikipedia)