The symbol "[]" is commonly known as square brackets. They are used in various contexts, including mathematics, programming, and writing. In mathematics, square brackets can denote intervals or group terms, while in programming, they often indicate arrays or lists. In writing, square brackets are used to add information or clarification within quoted material. For example, if a quote needs context, a writer might insert a word or phrase in square brackets to help the reader understand. This usage helps maintain the integrity of the original quote while providing necessary context.