OK is probably one of the most popular words, all over the world. Used for communicating face to face, but also, with technology.
But it was first used way back in the 1800's, and it was sort of a fluke, or actually, a language 'fad' as an abbreviation.
And these days, it's even MORE abbreviated, as you've probably sent (or received) just the 'K' back in a text..