Buddhist Jhanas, how best to describe them?

I’m conducting research into the phenomena of Buddhist Jhanas/Dhyanas, and am looking for a good place to start. In addition to primary sources that discuss what this phenomena is, how would you describe what the Jhanas are to a person unfamiliar with any sort of meditation practice? How do they differ across different sects/schools? How are they viewed sociologically or philosophically from OUTSIDE the lens of a practitioner or one who believes in the concept of enlightenment to begin with? TL; DR seeking primary source information on Jhanas/Dhyanas. What is their history? How do they differ across schools/sects? How would an outsider or an academic understand them? Thank you for your time.