In 1838, a fad for joke abbreviations took off in Boston. Most reference works say "OK" began there, short for "oll korrect," a silly misspelling of "all correct."
In the 1840 US election, supporters of President Martin Van Buren said OK stood for his nickname, "Old Kinderhook," after his hometown. That publicity seems to have spread the word across the United States.
It has been called the world's most spoken or written word.