This is the unit of currency in Fourecks.
Annotation, possibly blindingly obvious
The term probably parodies 'quid', a slang term for British pound. The pound (£AUS) was the unit of currency in Australia until supplanted by the dollar ($AUS) in the 1950's.
But given Terry's fondness for bad jokes, it could be a reference to the old joke about sub-aquean currency, in which a shark repays a cash loan by handing over an unwell ink-squirting cephalopod, saying "here's the sick squid I owe you".