In my linguistics classes, I ask students to define what a word is. They usually come up with some traditional definitions (more or less what you’re thinking right now). And that’s fine. This is not an easy question. Our department has a course devoted to the topic. But I’m going to start asking them if K is a word.
Consider the following exchange. It could appear on the internet or in texting.
Person 1: Maroon 5 is a great band.
Person 2: K.
Person 2’s response does not mean “OK”. On the contrary, I think K means roughly “I disagree with you but I’m not going to try to argue with you. I’m just going to drop it. My brusqueness, however, points out that your opinion is bad and I have won this battle by barely competing.” I’m not sure if the period is necessary (in written communication) or if it can be spelled in lowercase. But I’m sure these options carry meaning for some people:
Another choice is writing it with a question mark, which I think means “Do you understand? This is not up for discussion”.
Naturally, the linguists over at the Urban Dictionary have this one covered. Proceed with caution to that page though.
And Twitter knows how to use it: