An abbreviation of the year 2010. It follows a pattern that started in 2000 by abbreviating the year 2K, then 2K1, all the way until 2K9. In order to keep the term 3 characters long, though, X, the roman numeral for 10, is used instead of the actual number.
2KX, aside from the X, has NOTHING
to do with Roman numerals. Writing
2010 in Roman numerals would give you MMX.
Some person may think it looks cool if they write 2KX, even though companies who made the "2K" saying catch on are just going with 2K10 this year.