A One Turn Kill is achieved when a player wins a duel in the space of a single turn, as soon as said player has the appropriate cards in hand and has control over the duel. The One Turn Kill is similar to a First Turn Kill, but the latter is pulled off during the player's first turn, while an OTK can be accomplished at any point of the duel (meaning that FTKs are all OTKs, but not all OTKs are FTKs).
The second prerequisite of an OTKs is that it must consist of maximum 6 or fewer cards; the listed cards cannot include cards on your opponent's side of the field, cannot include cards that relate to indefinite chance (Such as "Dangerous Machine Type-6") and cannot include Seting cards that are part of the OTK. All of the cards of the OTK must have a reasonable chance of being drawn early, to be able to take control of the duel and win before being overwhelmed.
Here are all the lists of possible One Turn Kills: