Aos Si

The aos sí (/iːs ˈʃiː/, archaically /eːs ˈʃiː/), are the Irish name for "people of the mounds." These are among the fairy folk, in this case particularly fairies of the earth. The most commonly recognized name for these in folklore is leprechauns, while in literature they are frequently referred to as halflings or famously in Tolkien's works as hobbits.

Etymology
In Old Irish such beings were called aes sídhe (/eːs ˈʃiːðʲə/). As in nearly all Gaelic folklore, the term "fairies" carried a different connotation than in modern English, where it tends to refer almost exclusively to diminutive winged humanoids (see pixie). The Gaels understood the aes sídhe to be represented by a wide variety of shapes and sizes and different magical powers.

Most of the aes sídhe are the survivors or the descendants of the Tuatha Dé Danann, one of the ancestral races of Ireland were defeated in battle by the mortal Milesians and (in various mythologies) tricked, forced, or shepherded into the Otherworld or underground in the mounds dotting Ireland's landscape.