Demonstrative adjectives are words that are used to differentiate and identify specific objects, people, or ideas. They can also point out the distance between different objects and people. In addition to this information, they show feelings and attitudes toward the mentioned items.
In English grammar, this, that, these, and those are demonstrative adjectives.
For example:
This train conveys passengers to London.
I think that book is mine.
These cakes are very quick and easy to make.
Let me give you a hand with those bags.