what is the full form of OK ?

OK means Olla Kalla or Oll Korrect

OK (also spelled as okay, ok, or O.K.) is a word used to denote acceptance, agreement, approval, or acknowledgment. OK expand as Olla Kalla. It is a Greek word which means All correct. This is a very common word used in conversation when we agree with the other. 

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Complete explanation

OK (spelling variations include okay, O.K., and ok) is an English word (originally American English) denoting approval, acceptance, agreement, assent, acknowledgment, or a sign of indifference. OK is frequently used as a loanword in various languages. It has been described as the most frequently spoken or written word on the planet.[1] The origins of the word are disputed.

As an adjective, OK principally means "adequate" or "acceptable" as a contrast to "bad" ("The boss approved this, so it is OK to send out"); it can also mean "mediocre" when used in contrast with "good" ("The french fries were great, but the burger was just OK"). It fulfills a similar role as an adverb ("Wow, you did OK for your first time skiing!"). As an interjection, it can denote compliance ("OK, I will do that"), or agreement ("OK, that is fine"). It can mean "assent" when it is used as a noun ("the boss gave her the OK to the purchase") or, more colloquially, as a verb ("the boss OKed the purchase"). OK, as an adjective, can express acknowledgement without approval.[2] As a versatile discourse marker or back-channeling item, it can also be used with appropriate intonation to show doubt or to seek confirmation ("OK?", "Is that OK?"). 

The word is an abbreviation of ‘orl korrect’. It was coined in the USA and means ‘all correct’. The word was first used as a slogan during the presidential re-election campaign of Martin Van Buren (1782–1862) in 1840. Van Buren’s nickname was “Old Kinderhook”.

Back then, in Boston and New York abbreviations were the rage and words were misspelled deliberately. So a group of his followers called themselves the “O.K. Club”; this later went on to mean “oll korrect” and “ Old Kinderhook”.This is just one of the many slang words that have survived until today.

I hope that it is helpful for you !