Not a stupid question at all. Solo for this purpose means the only licensed pilot on board, you can have non flying passengers in the aircraft. A cross country is usually considered to involve an away landing, but as far as I know a planned flight with a defined turning point ought also to be acceptable. There is a theory that more than "x" miles from home is cross country, but I wouldn't like to argue that one with the CAA (I am supposing you are UK based)
BTW the 300 mile cross country should be done in one day, though mine was actually over two days due to bad weather, which was accepted by the CAA.