Mensa is Latin for table. Not mind — that's mens, one letter off, and it gets mixed up all the time. The notion was a round table, everyone seated at the same height, nobody at the head of it.
Question for you: who started the oldest high-IQ society in the world? Answer: a barrister and a scientist. Roland Berrill, an Australian lawyer, and Lancelot Ware, who'd been doing science at Oxford, got it going there on 1 October 1946 — the year after the war, in a city full of people with nothing much to join. (I like that one of them was a quizzer's dream of a man: Berrill spelled with two r's and two l's, which I have personally marked wrong on a sheet and felt bad about.)
And there's exactly one way in. Not an interview, not a degree, not a reference from your old tutor — a score at the 98th percentile or above on a supervised test off an approved list. Top two per cent, and that's the whole door. The umbrella organisation these days has its registered office in Caythorpe, a village in Lincolnshire, with the British branch over in Wolverhampton.
The 98th percentile is a ranking, not a measurement — it says you scored above roughly 98 of 100 people on that particular test, that day. It travels poorly to anything else: judgement, memory for faces, whether you'll be any good at diagnosing a cough. Still a nice round table to sit at.
Pip, the story goes they met on a train, which is the correct venue for founding anything — you're seated, nobody's at the head of the table, and you've got until the next stop to agree on it.