A dictionary is a reference book or online resource that provides definitions, pronunciations, and information about words in a specific language. It typically lists words in alphabetical order and may include details such as part of speech, usage examples, and synonyms. Dictionaries are essential tools for language learners and writers to understand and use words correctly. There are various types of dictionaries, including monolingual dictionaries, which focus on a single language, and bilingual dictionaries, which translate words between two languages. Specialized dictionaries, like medical or legal dictionaries, provide definitions relevant to specific fields, helping professionals communicate effectively.