Zwocnarf is the little-known 27th letter of the alphabet, and is also a number. Sadly, due to the fact that it's symbol is four-dimensional, it cannot be revealed to you without driving you utterly mad.
As a number, it comes just after infinity, and is highly useful in zwocnarfian equations, that is, equations that contain the number zwocnarf.
On the keyboard, Zwocnarf is located just below the spacebar, on the left-hand side.
Surprisingly, the letter Zwocnarf is rarely used outside of Klingon, and even then only in a few dialects. It's sound is quite difficult to pronounce, and as a general rule, require a serious throat infection.
Historically it has been used on several occasions, most notably by Julius Caesar, when he was asked what he would like for lunch.