In the Northern Kingdoms and Nilfgaard, when talking of races, one means mostly one of the civilized, humanoid races - humans, elves, dwarves, gnomes and halflings. Of these, humans and elves are capable of interbreeding, thus producing half-elves. Dryads are also a humanoid, but less civilized race.
While other intelligent and sentient creatures exist, they are much less similar to the aforementioned races than they are to each other, and thus are often thought of by people as monsters.