Acceptable, satisfactory, or in good enough condition; also used to show agreement or to check understanding.
Probably from a humorous 19th-century American fad of misspelling "all correct" as "oll korrect," shortened to "OK." It spread widely, helped by its use as a campaign slogan for U.S. president Martin Van Buren, nicknamed "Old Kinderhook" (OK).
This tiny word is one of the most recognized on Earth, yet it started as a joke spelling in a newspaper. Its rise shows how playful mistakes can become global language if they’re short, useful, and catchy.
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