What does X mean to you?

X of the A to Z Challenge

Honestly, I have run out of topics to write on as this challenge having written a blog nearly everyday! Therefore, my topic today is the very letter X!

X is one letter in the alphabet that means so many different things!
While it is used to make weird sounding words that are generally used in playing Scrabble, or make words that sound as though they start with Z rather than an X -for example, Xena (remember the warrior princess?) or Xenophilius Lovegood, or Xavier the letter X itself has several interesting facets and uses that no other letter of the alphabet has.

Here are a few uses of X

x - sizes are denoted in XL, XXL. Here X stands for Extra.
x - differentiator - The X-factor, The X-Men
x - Used as a multiple 2x, 3x etc. or used as the multiplication sign
x - cross mark/ incorrect
x - unknown variable in algebraic equations. This was always the dreaded letter back in school where the question to a complex algebraic equation was as simple as find the value of x!
x - In Roman language, X means 10
x - rated movies are meant for adults
x - represents the unknown or to cite an example - Person x

These are some of the uses of x I could think of.  Let me know in your comments if you can think of any more!