Having the ability to fulfill your desires (or to not fulfill them, if you don't want to for some strange reason). There are always degrees of freedom, we never have total freedom (or maybe we do when we die, idk), and we never have no freedom, but the most important marker, I guess, is being able to fulfill our desires. Maybe not ALL of our desires, e.g., do we not have the critical amount of freedom because we can't make out with Scarlett Johansson, or because we can't make a billion dollars, or perform psychokinesis? I'd guess no.