X = Christ as in Xmas X = extra as in XXL X = a kiss at the end of a message (not an abbreviation though, just a symbol)

I can only think of five that are common: Xmas = Christmas X-walk = crosswalk FX = effects i.e. sound fx PX = post exchange (a store on a military base) BX = base exchange (a store on a military base) And one less common one: XTC = ecstacy

X-rated is another

The first one that comes to mind is probably xoxo 😂 it stands for hugs and kisses. However its not an abbreviation by definition 😂