Parenthesis

Parenthesis: an amplifying or explanatory word, phrase, or sentence, inserted in a passage from which is usually set off by punctuation; remark or passage that departs from theme of discourse; one or both of the curved marks (  ) used in writing and printing  to enclose a parenthetical expression or to group a symbolic unit in a logical or mathematical expression

Example: "For the vagabond-voyeur (and for travelers voyeurism is irresistible), nothing is not for notice, nothing is banal, nothing is ordinary: not a rock, not the shoulder of a passer-by, not a teapot."
- Cynthia Ozick, "The Shock of Teapots"