An adjective for something in, or from, the northeast part of a country, island, or area: northeastern Spain, the northeastern suburbs, a northeastern accent. It pins you to that corner, not to the whole north and not to the whole east. You can use it for any map, not only the United States — though when Americans say the Northeastern states they often mean that named US region. Compared with Northeast as a place-name, northeastern is the everyday describing word: it stays an adjective. Though actually speakers sometimes swap it with northeast as if they were the same (northeast France / northeastern France); both are heard, and the -ern form slightly more often sits before a noun as a tidy label. It is ordinary geography language, not poetic.