As an adjective,
"okay" means "adequate," "acceptable" ("this is okay to send out"),
"mediocre" often in contrast to "good" ("the food was okay"); it also
functions as an adverb in this sense. As an interjection, it can denote compliance ("Okay, I will do that"), or agreement ("Okay, that's good"). As a verb and noun
it means "assent" ("The boss okayed the purchase," and, "The boss gave
his okay to the purchase.") A versatile discourse marker (or back-channeling item), it can also be used with appropriate voice tone to show doubt or to seek confirmation ("Okay?" or "Is that okay?").
The term is often associated with a sudden traumatic loss of consciousness caused by a physical blow. Single powerful blows to the head (particularly the jawline and temple) can produce a cerebral concussion and cause a sudden, dramatic KO. Body blows, particularly the liver punch, can cause progressive, debilitating pain that can also result in a KO.