Jessica Livingston talked early days of YC, and especially weekly dinners. As far as I can tell, what YC reproduced, in part, is borrowed from the old Oxford-Cambridge tradition and, starting in ~1700s, adopted by most Ivies: the Junior College Room (JCR).

The Junior Common Room is a derivative of the Common Room🔎.

It's interesting to note JCRs are virtually nonexist at big universities. There is no JCR at Big University.

JCRs are little reading rooms—a couch, round tables chairs, a wall of books. Each inside a "College" (or House), they are used to host little get-togethers, talks, wine & cheese receptions, tea (in England), high tea.

They are extensions of the Common Room. In English university tradition, the Common Room is where all the faculty, fellows, and research staff come together for afternoon tea. It sounds like a break room but it isn't.

A break room is designed to get you out of it. Just a break. No puttering or loitering allowed.

Common Rooms, on the other hand, might entertain or host members for an entire afternoon, several hours, into the evening. You might meet a colleague for tea at 4 and roll the discussion until some wine and cheese reception happenining at 7pm, then stay on until 9 or 10pm.*