A demonstrative pronoun points to and identifies a noun or a pronoun. "This" and "these" refer to things that are nearby either in space or in time, while "that" and "those" refer to things that are farther away in space or time.

The demonstrative pronouns are "this," "that," "these," and "those." "This" and "that" are used to refer to singular nouns or noun phrases and "these" and "those" are used to refer to plural nouns and noun phrases. Note that the demonstrative pronouns are identical to demonstrative adjectives, though, obviously, you use them differently. It is also important to note that "that" can also be used as a relative pronoun.

In the following sentences, each of the highlighted words is a demonstrative pronoun:

This must not continue.

Here "this" is used as the subject of the compound verb "must not continue."

This is puny; that is the tree I want.

In this example "this" is used as subject and refers to something close to the speaker. The demonstrative pronoun "that" is also a subject but refers to something farther away from the speaker.

Three customers wanted these.

Here "these" is the direct object of the verb "wanted."

The pronouns this, that, these, and those may also be used as adjectives:

This car is better than that car.