Context clues are hints in the text that help readers understand unfamiliar words based on the surrounding context. There are three main types of context clues: definition clues explicitly define the word, synonym clues use a word with a similar meaning, and antonym clues use an opposite word. Authors include these context clues so readers can logically infer the meaning of new words based on surrounding context without needing a dictionary. Mastering context clues improves reading comprehension.