https://astralcodexten.substack.com/p/nick-cammarata-on-jhana

Buddhists say that if you meditate enough, you can learn to enter a state of extreme bliss called jhana.

(there are many different jhana states - there's a discussion of the distinctions here - but I'm lumping them together for simplicity. For attempted explanations of why jhana should exist, see here and here.)

Jhana is different from enlightenment. Enlightenment changes you forever. Jhana is just a state you can enter during meditation sessions, then leave when the session is over. Enlightenment takes years or decades of work, but some people describe reaching jhana after a few months of practice. Hardcore Buddhists insist that jhana is good only insofar as it serves as a stepping stone to enlightenment; others may find extreme bliss desirable in its own right.

Nick Cammarata of OpenAI sometimes meditates and reaches jhana. I've found his descriptions unusually, well, descriptive: