These creatures are called tomtar, or nisser/nissar, and is causing a bit of confusion when they meet the language English. They are basically vättar (Norse; vættr) and among the beings sometimes named tusser (from þurs - yes, giants I know, which may seem odd, but jättar isn't always giant size beings) and with valkyrjur as distant cousins (though that's more outside the Nordic region, among other Germanic peoples where they were more feared and thought of as bringers of horrible news).
Suffice to say, they're not elves, as English speaking tend to name them. Álfar/alver (which are elves) is something else (see Norse mythology). There are no fitting terms for these underworld peoples in English - or I have at least never found any. They're not fairies. The equivalent of fairies are älvor, huldran, skogsrået and näcken; beautiful, tempting, dangerous and positively ethereal in comparison to the other beings.
There's a confusion of terms between the Nordic languages and English, simply because there is a difference in folklore between us. And then there's Tolkien. His mixed salad between the two folklores plus mythology has added to contemporary confusion.