A dictionary is a reference book that provides meanings, pronunciation, etymology, and other information about words. It is a collection of words and their definitions, typically listed in alphabetical order. Dictionaries can be general, covering all areas of language, or specialized, covering a particular subject or language. Some dictionaries also include usage examples and synonyms or antonyms for the words they define. They are used to help people understand and learn the language, as well as to find the correct spelling and meaning of words.