For the round brackets used in punctuation, often called parentheses, see bracket.

In rhetoric, a parenthesis (plural: parentheses; from the Greek word παρενθεσις) is (according to the Oxford English Dictionary)

"An explanatory or qualifying word, clause, or sentence inserted into a passage with which it has not necessarily any grammatical connexion, and from which it is usually marked off by round or square brackets, dashes, or commas."

Examples

Consider this sentence:

Karl, a great singer, was not a good dancer.

The phrase a great singer, set off by commas, is a parenthesis.

A dog (not a cat) is an animal that barks.

The phrase not a cat is a parenthesis.

Addressing a person by name can also be parenthetic, as in: Please, Duncan, come here!

Punctuation

By extension, the word parentheses, seldom used in the singular, has come to refer to the round brackets in which a parenthesis is often enclosed in writing. See bracket for an account of these punctuation marks.