This is a society where members "duel" each other to climb rankings. The ultimate goal is to be the best "duellist" in the university. Duels can be almost any zero-sum game.
If you like playing very obscure games that you've secretly been practising for weeks against on unwitting opponents or if you're the kind of person who'd eat a scotch bonnet for 50 pence then Duel Society might appeal to you! In a nutshell, you compete against other members in games to climb the rankings. These games can be practically anything you think of. Standard things like chess, table tennis, or maybe you'd like to do some arm wrestling, a staring contest? Perhaps you've been desperate to test your stomach capacity for pie? Have you secretly been mastering the art of mashing a button as fast as possible, or maybe you just want to moo in someone's face until they crack?
Strictly, a duel can be any (reasonable) zero-sum game. Draws are fine, but if there is a winner in a duel, there must be a corresponding loser. We are competing against each other, not with each other.
Now you could just participate in duels without giving notification; this society isn't required to challenge someone at some game or competition. But what this society provides in addition is a ranking system. The results of duels will be collated and used to calculate and update a live ranking of every member. The method of calculation is currently anticipated to be Glicko-2, but this is subject to change. There will almost certainly be some incentive given to achieve high rankings. More information on this will be given once these incentives are formally established. At the very least, you get the bragging rights of being the most literal jack-of-all-trades in Cambridge.
The society will also hold organised tournaments at regular intervals that members may choose to enter. These tournaments will have some sort of restriction or theme in their duels that will be announced ahead of time. Winners of these get the satisfaction and glory of first place, maybe a prize, and also get their overall rankings adjusted accordingly.