Squid

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 octapodean, saying "here's the sick squid I owe you".