Donut holes are small fried dough pastries, strongly associated with the American donut tradition.
Their name is largely a joke, implying that donut bakers must produce a large number of unneeded "holes" from all the donuts they produce. In actual practice, most fried donuts are produced with circular molds, and there is no leftover collection of "holes" needing to be fried and sold separately.
Baked donuts, which might be cut from a sheet of dough, can and do produce leftover dough.
In any case, they are fun bite-sized pastry that is available in many flavors and styles. Compare Greek loukoumádes and German quarkbällchen.