2KX is an abbreviation of the number 2010... where 2K refers to 2000 (K being the scientific notation of 1000) and X is the Roman numeral 10.
Note the roman numeral for 1000 is M, so 2MX, MMX and KKX are equivalent.
"Welcome to this extravaganza to see in the new year, 2KX... yes 2010 is finally here after a whole years wait!"
person 1: Did you know that 2KX is the roman numeral for 2010.
person 2: Actually, that would be MMX. 2KX is a mixture of Roman and engineering notations.
person 1: So the definition of 2KX on UrbanDictionary was wrong?
person 2: Yes, whoever wrote that was a muppet...