A joint win is a win split between multiple parties.
In order to joint win, all of the roles that wish to joint win must fulfill their win conditions at the same moment. The most split joint win possible is with the mafia, lyncher, warlock, fool, and survivor.
There must be 3 mafia. The warlock must have one prediction already and predict the fool, while the lyncher's target is the fool and they lynch the fool. While this is highly unlikely, it is still possible.
Some roles can also joint-win with the village. Survivor is the obvious example, another example of such would be a lyncher whose target is a hunter, and upon lynching that hunter he/she shoots the last mafia. Also, lyncher joint-wins with town if his/her target is converted by yakuza, and that target is the last mafia remaining and gets lynched.