general mechanisms electric-magnetic duality, Montonen-Olive duality, geometric Langlands duality string-fivebrane duality string-QFT duality QFT-QFT duality: effective QFT incarnations of open/closed string duality, relating (super-)gravity to (super-)Yang-Mills theory: Seiberg duality (swapping NS5-branes) The term S-duality can mean two different things: in mathematics it is short for Spanier-Whitehead duality : monoidal duality in the stable homotopy category; in physics it denotes a...