ASCII Character [Opening bracket
Square brackets [ and ] are also called simply "brackets" (US), as well as "crotchets", "closed brackets", or "hard brackets". Square brackets are often used to insert explanatory material or to mark where a [word or] passage was omitted from an original material by someone other than the original author, or to mark modifications in quotations. Brackets are used in many computer programming languages, primarily for array indexing. But they are also used to denote general tuples, sets and other structures, just as in mathematics.