Concept of Pancha Janah in Hinduism is found in the Aitareya
Brahmana.
Aitareya Brahmana explains the term pancha janah as gods,
gandharvas (including apsaras), human beings, serpents and departed ancestors.
As per Sayana, the Pancha Janah are the five social groups –
the four castes – Brahmin, Shatriya, Vaishya, Shudhra – along with Nishada
(barbarians) as the fifth.
Yaska in his Nirukta enumerates the five classes as gods,
human beings, gandharvas, asuras and rakshasas.
As per some scholars, the pancha janah included people
staying on the four quarters of the earth and those residing in the central
part.
There is also a belief that the term was used to refer to the
five tribes of Anu, Druhyu, Turvasu, Yadu and Puru in ancient Hindu world.
There is another interpretation pancha janah are the five
divisions of Devas – Purva Devah, Mura Devah, Sisna Devah, Sura Devah And
Vishwa Devah.
Notes take from - Encyclopedia of Hinduism Volume VIII - IHRF - page 3