In CycL, collections are used to talk about general concepts rather than individual things. For example, in Cyc, #$Dog is the collection that contains all dogs. (In contrast, #$Snoopy is a particular dog, i.e. an instance of the collection #$Dog.) Collections are like sets except that, unlike a set, a collection can gain or lose membership over time: every time a new dog is born, the collection #$Dog gains a new member.
