In rhetoric, a parenthesis (plural: pfrom the Ancient Greek word παρένθεσις parénthesis 'injection, insertion', literally '(a) putting in beside') or parenthetical phrase is an explanatory or qualifying word, clause, or sentence inserted o a passage. The parenthesis could be left out and still form grammatically correct text. Parentheses are usually marked off by round or square brackets, dashes, or commas.