1. (REN-it, REN-et) An ingredient from the stomachs of animals or from plants or microbateria that is used to make cheese.
2. (REN-it, REN-et) A completely ficticious rodent described on a hoax site which encourages people to save the ficticious creature.
That dumbass said he stopped eating cheese because he read online that they boil-alive these little rodents called rennets to make it. - What a moron - there's no such thing.