E may refer to any of the following:
1. Short for Enlightenment, E is a desktop windows manager for X Windows, first developed by Carsten Haitzler in 1997. Enlightenment is capable of running by itself or in conjunction with other desktop environments, such as GNOME and KDE.
4. E is an abbreviation of exponent.
5. With the ESRB (Entertainment Software Rating Board), an "E" rating is short for "everyone" and is a game meant for players of all ages.
6. With a regular expression, \e matches an escape.
8. In the phonetic alphabet, "E" is often pronounced as "echo."
9. Euler's number (e) is a mathematical irrational number that's approximately equal to 2.71828 and is helpful in finding slopes in Calculus and working with compound interest. When working with a scientific calculator, this number can be entered by pressing the "e" button.
If the "E" key is not working on the keyboard, see: Some of the keys on my computer keyboard aren't working.