A collective noun is used to refer to a group of people or things. The opposite of a collective noun is a countable noun. If I say there is a flock of birds, you really don't know how many I mean...
Collective nouns are words for a group of like nouns. Examples: A flock of sheep. A stable of horses A troop of monkeys A troupe of actors A panel of experts A crowd of onlookers A fleet of cars A...