Demonstrative adjectives (often categorized as demonstrative determiners instead in more modern grammars) are words used before nouns to indicate their relative distance (literal or figurative) from the speaker or writer (e.g., “I like this hat better than that one”).
The English demonstrative adjectives/determiners are this, that, these, and those. This and these indicate something relatively close to you, whereas that and those indicate something farther away. The same words are used as demonstrative pronouns.