square bracket

WordReference Random House Unabridged Dictionary of American English © 2025

square′ brack′et, 

1. Printing bracket (def. 3).

• 1885–90

Collins Concise English Dictionary © HarperCollins Publishers::

square bracket noun

1. either of a pair of characters [ ], used to enclose a section of writing or printing to separate it from the main text
2. Also called: bracket either of these characters used as a sign of aggregation in mathematical or logical expressions indicating that the expression contained in the brackets is to be evaluated first and treated as a unit in the evaluation of the whole