Such nouns are not compulsory, and are in general not widely used. A pride of lions can equally well be referred to as "a group of lions", "a bunch of lions", "a family of lions", "a number of lions", "a herd of lions", "some lions", etc.
The exact definition of a genuine collective noun is debatable. Some people say that words like "set" or "flock", which are not subject-specific, are also collective nouns.
Many nouns used are colourful, or even fanciful; this originated in an English hunting tradition (of uncertain origin) for giving poetic names to prey. (The phrase "terms of venery" is an archaic synonym for collective nouns - "venery" in this context meaning the "act of hunting"). For this reason, most collective nouns refer to animals.
Interest in collective nouns has always remained high, and the neologism of candidate collective nouns has been a pastime of many writers ever since. Some have achieved an entry in a respected dictionary, the vast majority have not. Some collective nouns have been circulated on websites for humourous reasons. In at least two cases (an "abomination of monks" and "a court of kangaroos") some authoritative resources allege them to be accurate, however research has proved these to be spurious as well.
Some alternatives for collective nouns can be clearly traced to the evolution of pronunciation in different areas (hence a "parcel of hogs" and a "passel of hogs").
Several collective nouns perform double, triple or even more duties. "Herd" is a legitimate collective noun for dozens of animals and (rather curiously) the mythical fairy. Also interestingly, "herd" can be used with wild horses and domestic cattle, but not with domestic horses. Likewise, "flock" is a generic collective noun for all sorts of flying birds. The all-time champion collective noun is "set", for it can legitimately be used as a collective noun for a vast number of concepts (a set of ideals, plans, ambitions, principles, objectives, mathematical objects, etc) or inanimate (typically manufactured) objects (knives, spoons, keys, dinnerware, manuals, etc).
The collective nouns here generally can be used to describe any sized group of the relevant subject. Occasionally they can only be used to describe the subject performing a specific action; eg. a "paddling of ducks" only refers to duck on water. Certain nouns have been excluded from this list because the collective noun is too highly specific and/or could be used to describe a single subject. A single cow can "stampede" (an unusual, but legitimate usage) and a single committee member can conceivably constitute a "quorum".
All of the collective nouns presented have been verified in one or more dictionaries, except where noted as "spurious" or "uncertain". English usage is, of course, in a constant state of evolution, hence the denotation of "uncertain" should not be taken to mean that the noun is categorically wrong, but only that no verification has been found (as yet) in a dictionary.
Other misinterpretations are included as well; some on-line resources give "rookery" as a collective noun for seals, penguins or herons, however this is incorrect. The term only refers to the breeding territory itself, and not to the collection of animals.
A significant number of collective nouns involve what must be considered "non-standard" usage of certain words. Some of the examples given for birds are quite fanciful; eg. "A murder of crows", "an exaltation of larks". Nearly everyone would be familiar with the term "library" as it pertains to books, but few would expect to see it as a collective term for any set of books, anywhere (most would assume it to mean a building or room containing books). However this usage (admittedly obscure) is legitimate and is thus included.
Several of the collective nouns presented are specifically regional (it is unlikely that a "disworship of Scots" was used in Scotland with any frequency). Certain examples defy logic; ferrets are known to be fiercely solitary animals, yet two collective nouns are known to exist ("business" and the old Saxon "fesnying"). This article does not attempt to provide etymologies; these can be found in a dictionary of etymology. Do there exist any freely accessible dictionaries of etymology on the Web?
Collective nouns sorted by subject
Collective nouns sorted by collective term
Collective nouns for people
Collective nouns for mammals, non-human
Collective nouns for birds
Collective nouns for reptiles and amphibians
Collective nouns for fish, invertebrates and plants
Collective nouns for objects and concepts
The collection of genuine and spurious collective nouns has proved an interesting diversion for many website writers: