What is OK short for?

The most popular theory is that OK comes from ‘oll korrect’, a deliberately misspelled writing of ‘all correct’. It was popularized in Boston newspapers around the 1840s when it was fashionable to go around spelling things incorrectly for humorous effect. Legend also has it that New York Democrats later adopted the abbreviation to promote their candidate Martin Van Buren – the initials ‘OK’ were derived from his nickname, Old Kinderhook.

Now you know. :)