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. Unicorns are a sentient race in the witcher universe. As witchers are mutants, they are sometimes also considered to be a separate "race".
In the role-playing game, the word "race" is used to refer to playable creatures - humans, elves, dwarves, gnomes, halflings, witchers and dryads.
In the game, the only playable character is the witcher Geralt. Witchers are arguably a race unto themselves, but the word "race" is used mainly to distinguish humans from non-humans. Races mentioned include elves, dwarves and gnomes.