Yaksha is the name of a divine group . The lord of the direction of North, Kubera is their chief. Many puranas mentioned Yakshas as follwers of Indra in his wars against the demons. In ahaabhaaratham too, this race is mentioned many times. Yama stood before Yudhishthira in the form of a yaksha while testing him in the forest.
Other divine groups are Siddha, Saadhya,Gandharva,Garuda,Naga,Kinnara,Kimpurusha,Vidyaadhara etc.