Demonstrative pronouns are words used to point to specific things or people. The main demonstrative pronouns in English are this, that, these, and those. This and these refer to items that are close in distance or time, while that and those refer to items that are farther away. These pronouns help clarify which nouns are being discussed without repeating them. For example, instead of saying "the book" multiple times, one can say "I like this book" or "I prefer those books." This makes communication clearer and more efficient.