An exclusive (especially of women) Gentlemen's Club on Esoteric Street in Ankh Morpork, frequented by Death in Thief of Time. There might be a wormhole through the Multiverse from the library here to that of White's (or perhaps Boodle's) in London.
Rule 34b allowed female members of the family or respectable married ladies over the age of 30 to be entertained for tea in the Green Drawing Room between 3:15 and 4:30 pm but one member of staff must be present at all times.
"Rule 34" is accepted shorthand on the Internet for "If it exists, somebody somewhere has made porn of it".
Rule 34b is a sub-clause which states:"If porn has not been made of an object that has been Rule34'd, porn will be made of this object as soon as your request is processed."
Others define 34b as a situation where, if it exists, some sickeningly twee person has done a My Little Pony: Friendship is Magic crossover version of it, which is classed as pornography of a different and even more revolting sort.
There is a very long list of sub-clauses for Rule 34. ().
As with the naked nearly-mud-fight between Angua and Sally in Thud!, is this another subtle little dig at writers of slashfic?