Actually, FLOSS is more precise, given the "L" coming from "libre" in castilian (spanish now a days) referring explicitly to freedom. But it so happen open source != free/libre software, therefore open source usually disregard the philosophic aspect of freedom, which might turn against the users interest, which is what GNU guys were trying to prevent all along, because focusing in the practical aspects, without any concern on the principals behind, actually do have implications on the software itself and its usage.