writing - When we write, do we have to write "OK" instead of "Ok" or are both correct?

I'm confused when I have to write "Ok" in a writing, because I don't know if "OK" and "Ok" are both orthographically correct or just one is.

Answer

OK is the abbreviation for oll korrect or orl korrect representing all correct. There are numerous explanations for the origin of the expression as suggested by the linked Wikipedia article.

You don't write Usa or USa for USA because USA is the abbreviation for the United States of America.

However, there are many forms of abbreviations in English and there is no hard-and-fast rule. For example, you abbreviate mister to Mr. or Mr and Doctor of Philosophy to PhD.

You could write Ok or ok in a text message or informal writing, but you should use one of the following three in formal writing. I would prefer OK to O.K..

OK

okay

O.K.