Homenum Revelio is a spell used to reveal where and when someone is hiding useful for when you are playing hide and sick and when you whant to have a conversation in a room but you don't know if someone is there.

It doesnt appear in the harry potter movies but it is a similar spell to what Hermione used is the Grimmauld Place which is the Fidelius charm.

There isn't a record is what year of Hogwarts you use the Homenum revelio spell.