Brackets and ellipses are punctuation marks that serve specific purposes. Brackets are always used in pairs and can enclose optional or explanatory information in a sentence, provide the full name of an abbreviation, or indicate chapter and page numbers. Square brackets enclose explanatory or missing material in quotations. Ellipses indicate a pause, unfinished thought, or omitted words. They are commonly used to shorten long quotations or show a character trailing off.