If something is inedible, you cannot eat it — or you really should not. The usual reasons are that it tastes too bad, or that it would make you ill or even kill you. A berry, a mushroom, or a plant can be inedible because it is poisonous. Food can also be inedible because it has gone off, or because it was cooked so badly that nobody can get it down. People say this about real food more than about things that were never food, like wood or plastic, though you will hear that joke too. It is a fairly ordinary adjective, a little more careful than just 'you can't eat that'. Though actually, some careful speakers like a split: they keep inedible for things that are not food, or that are unsafe, and they use uneatable when the cooking is just awful. In everyday talk, a lot of people use inedible for both, and listeners still understand.