parenthesis

A clause, phrase or word which is inserted (usually for explanation or amplification) into a passage which is already grammatically complete, and usually marked off with brackets, commas or dashes.

How expressive this little parenthesis: "Sakuntalâ makes a chiding gesture with her finger"!

Either of a pair of brackets, especially (mainly US) round brackets, ( and ) (used to enclose parenthetical material in a text).

There be five manner of points and divisions most used among cunning men; the which if they be well used, make the sentence very light and easy to be understood, both to the reader and hearer: and they be these, virgil,—come,—parenthesis,—plain point,—interrogative[…] it is a slender stroke leaning forward, betokening a little short rest, without any perfectness yet of sentence.

Whoever introduced the several points, it seems that a full-point, a point called come, answering to our colon-point, a point called virgil answering to our comma-point, the parenthesis-points and interrogative-point, were used at the close of the fourteenth, or beginning of the fifteenth century.

A digression; the use of such digressions.

Mr. Trevanion was one of those talkers, who are too much engrossed with their own subject matter to have much attention to bestow elsewhere; with them silence is attention. Ethel's wandering eye, and lip, tremulous with its effort to speak, would never have attracted his notice. To his utter astonishment, she interrupted a parenthesis, as brilliant as the rocket which it depicted, by saying,— "Mr. Trevanion, I do not know what you will think of my boldness, but I must speak to you."

Ryan Bingham (George Clooney): I thought I was a part of your life. Alex Goran (Vera Farmiga): I thought we signed up for the same thing[…] I thought our relationship was perfectly clear. You are an escape. You're a break from our normal lives. You're a parenthesis. Ryan Bingham (George Clooney): I'm a parenthesis?

Such brackets as used to clarify expressions by grouping those terms affected by a common operator, or to enclose the components of a vector or the elements of a matrix.