This, that, these and those are a class of determiners which indicates proximity in space or time to the speaker (or writer). This and these refer to things that are close to the speaker while that and those refer to things further away.

E.g., No one cares these days.

They didn't have computers in those days.

When this, that, these and those are used before a noun (this hat, that house), they are usually referred to just as demonstratives. You may also see the the term demonstrative adjective - it is the same thing.

These words can also be used as pronouns; this group is known as demonstrative pronouns.

I don't like these.

Pass me that.

Can I borrow this?

Those are nice.

In these examples the words act as subjects or objects, so they are pronouns.