An ordered account of what a collection holds. A catalogue does not hold the things; it makes them findable.
Greek katalogos (a list, an enrollment), from katalegein (to count off, to recount), from kata- (down, thoroughly) + legein (to say, to count).
The list is not the treasury — a catalogue can be complete and correct while everything it describes sits somewhere else entirely, because its whole job is pointing rather than possessing, and losing it loses the way back in, not the collection itself.