At least in the sport
does not necessarily have anything to do with unconsciousness
. A KO, or "knockout
" is scored when a boxer is counted as being down by the referee and this leads to the end of the fight.
Traditionally, this means the boxer is knocked on his butt and doesn't get up before the referee counts to ten. Very often though the entire count is not given, or the ref will stop the bout immediately after the knockdown. This is done so that the ringside doctors can quickly enter the ring and make sure the fighter is ok. Knockouts in modern boxing rarely involve the boxer becoming completely unconscious, or truly "knocked out".
On the other hand, KO is also used in boxing statistics to represent the number of stoppages a boxer has won. See my WU on TKO for a discussion of what counts as a Technical KO and a real KO. So, in this sense, "KO" represents a situation where a boxer did not even get knocked to the floor.