Square brackets, also known as brackets or box brackets, are punctuation marks that look like this: [ ]. They are used in writing to enclose additional information, clarifications, or comments that are not part of the original text. For example, in academic writing, square brackets can indicate changes made to a quote for clarity or context. In programming, square brackets are often used to denote arrays or lists, such as in languages like Python or JavaScript. They can also indicate optional elements in syntax or commands. Overall, square brackets serve to enhance understanding and organization in both written and coded content.