The vast majority of humanoid races in Auriin shared a common ancestry, some more distant than others. This blood bond allowed couples of two different races to produce offspring, who inherited characteristics of both parent races. While such individuals weren't usually considered to belong to some different third race in any literal sense, they were often given labels to describe their genetic makeup. These labels often consisted of the prefix "half-", followed by one of the parent races, usually the one most apparent in the physical appearance of the child.
The vast majority of such half-breeds were half Human. Being the most pervasive of the Yeula, Humans found their way into couplings with a wide range their kin, from Elves to Dwarves, and even Orcs. It was even posited by some - mostly bards in seedy taverns - that Dragonborn were the product of the alliance between Humans and Dragons in a rather literal sense.
On the other hand, Gnomes were thought to have stubbornly immiscible blood, making them incapable of interbreeding with the vast majority of other races. There were rumors of Halfling families with Gnomish blood, but the only half-gnomes noted in the histories were half-human.