Tous and Tout
When do you use one and when do you use the other?
tout - masculine singular
tous - masculine plural
tout le monde - everybody (you would think it's tous but it's masculine singular so just tout) :)
Note that "everybody" is also singular in English: it's "everybody/everyone is OK", not "everybody/everyone are OK", so tout actually makes more sense coming from English than tous.
Trivia: "Bonjour tout le monde!" is on the Voyager recording, zooming out into space.