A collective noun is the name of a collection of people, animals, or things that can be spoken about as a whole or group.  One of the many oddities (and annoyances) in the English language is the number of different collective nouns that exist.  Some of these collective nouns are likely to be familiar to you, for example: ‘group of people’, ‘group of ideas’, ‘group of children’ etc.  The word “group” is probably the most common collective noun in English.  But there are many, many more collective nouns in English and most of the other collective nouns are used specifically to describe one group of objects or animals.  I will give a number of examples of collective nouns below for you can see just how varied these collective nouns can be.  Before looking at these it is important to be clear that collective nouns are different from mass nouns.  As a reminder, mass nouns (also called non-count or uncountable nouns) are nouns in which the object that is being talked about is treated as one undifferentiated unit, rather than a collection of individual units taken as a whole.  For example rice is a mass noun.  We always talk about rice as a whole (i.e. a bag of rice, a pound of rice, a bowl of rice) we never talk about rices as individual units.  Collective nouns are used to describe countable items (nouns that can be made plural).  Collective nouns can be seen as individual units, multiple or plural units, and collective or group units.

Here is an example of how to use a mass noun:

lion                            –      lions                               –     pride of lions
(noun)                       –     (plural  form)                  –     (mass noun)
one animal                –    multiple animals              –    a group of animals

Now, here is a list of some common, uncommon, and funny collective nouns in English:

Animal related:
a flock of birds
a litter of pups
a prickle of porcupines
a litter of cubs
a pack of dogs
a colony of beavers
a gaggle of geese
a family of otters
a huddle of walruses
a herd of deer
a culture of bacteria
a swarm of bees
a bed of clams
a school of cod
a herd of dinosaurs
a mess of iguanas
a mob of wombats
a pod of pelicans

People related:
a troop of boy scouts
a team of athletes
a panel of experts
a crew of sailors
a band of robbers
a troupe of performers
a crowd of onlookers
a curse of painters

‘Thing’ related:
a fleet of cars
a pair of shoes
a fleet of ships
an anthology of stories

In summary we use collective nouns to talk about nouns that come in groups.  If you don’t know the specific collective noun name for a group of things you can always use the word “group” in front of the noun, i.e. ‘a group of cars’ is correct English, but ‘a fleet of cars’ is more correct English.  Here is a website that gives a more extensive list of collective nouns in English if you would like to learn more: http://users.tinyonline.co.uk/gswithenbank/collnoun.htm.