OK Definition
An utterance expressing exasperation, similar to "all right!"
Acronym of Oklahoma, a state of the United States of America.
Origin of OK
Of unclear origin. Wikipedia lists several possibilities. it may be an abbreviation of a comical spelling of "all correct" as "oll korrect", such as first appeared in print in The Boston Morning Post on March 23, 1839, as part of a fad for similar fanciful abbreviations in the United States during the late 1830s.
From Wiktionary
Abbreviation of oll korrect slang respelling of all correct
From American Heritage Dictionary of the English Language, 5th Edition