a support, as of metal or wood, projecting from a wall or the like to hold or bear the weight of a shelf, part of a cornice, etc.

a shelf or shelves so supported.

Also called square bracket. one of two marks [ or ] used in writing or printing to enclose parenthetical matter, interpolations, etc.

Mathematics. brackets, parentheses of various forms indicating that the enclosed quantity is to be treated as a unit. (loosely) vinculum (def 2). Informal. an expression or formula between a pair of brackets.

a grouping of people based on the amount of their income: the low-income bracket.