He’s not the great sage many claim him to be, of course, but in some cases, George Orwell got it spot on. In Notes on Nationalism (1945), he provides the following useful distinction:
By “nationalism” I mean first of all the habit of assuming that human beings can be classified like insects and that whole blocks of millions or tens of millions of people can be confidently labelled “good” or “bad.” But secondly — and this is much more important — I mean the habit of identifying oneself with a single nation or other unit, placing it beyond good and evil and recognizing no other duty than that of advancing its interests. Nationalism is not to be confused with patriotism. Both words are normally used in so vague a way that any definition is liable to be challenged, but one must draw a distinction between them, since two different and even opposing ideas are involved. By “patriotism” I mean devotion to a particular place and a particular way of life, which one believes to be the best in the world but has no wish to force on other people. Patriotism is of its nature defensive, both militarily and culturally. Nationalism, on the other hand, is inseperable from the desire for power. The abiding purpose of every nationalist is to secure more power and more prestige, not for himself but for the nation or other unit in which he has chosen to sink his own individuality.
Orwell, of course, wrote favorably about patriotism from the socialist left in his essays in “The Lion and the Unicorn: Socialism and the English Genius” (1941), most notably in England, Your England.