A collective noun (集合名詞)names a group of peole:

people , places, things, animals

A collective noun looks like a singular noun .It behaves like a singular noun too.

It is? a noun phrase.

The chameleon ate a group of flies.

a ,? an and the

we use the for uncountable nouns.

the milk , the water, the meat

We also use"the " before an adjective that is used to desribe a person.

The rich(the people who are rich)

The? poor

The injured

The elderly

The word this and that are adjective too.They also come before nouns. We call them demonstratives.