OK is an American English word denoting approval, acceptance, agreement, assent, acknowledgment, or a sign of indifference.
American English, also called United States English or U.S. English, is the set of varieties of the English language native to the United States.
Kirk Franklin - OK by Kirk Franklin
OK is frequently used as a loanword in other languages.
A loanword is a word adopted from one language and incorporated into another language without translation.
KO Home Alone | OK K.O.! Let's Be Heroes | Cartoon Network by Cartoon Network
As an adjective, OK principally means "adequate" or "acceptable" as a contrast to "bad" ; it can also mean "mediocre" when used in contrast with "good".
As an interjection, it can denote compliance, or agreement.
In linguistics, an interjection is a word or expression that occurs as an utterance on its own and expresses a spontaneous feeling or reaction.
It can mean "assent" when it is used as a noun or, more colloquially, as a verb.
A noun is a word that functions as the name of some specific thing or set of things, such as living creatures, objects, places, actions, qualities, states of existence, or ideas.
As a versatile discourse marker or back-channeling item, it can also be used with appropriate voice tone to show doubt or to seek confirmation.