nonrestrictive

Nonrestrictive describes a modifying clause or phrase that adds information about a noun but is not essential to identify it. The information is supplementary; removing it does not change the basic reference of the sentence.

In English, nonrestrictive relative clauses provide extra detail and are typically set off by commas. They usually begin with which, not that. Example: The book, which has a blue cover, is mine. Changing which to that would yield a restrictive, essential clause: The book that has a blue cover is mine.

Nonrestrictive appositive phrases also supply non-essential information about a noun. Example: My brother, a doctor, lives in Boston. Here the appositive "a doctor" renames the noun but is not required for identification.

Punctuation marks the distinction: nonrestrictive material is offset with commas; in less formal writing, dashes or parentheses may mark it. The distinction affects meaning and emphasis and is important for clarity in scholarly and formal styles.

Some languages do not have a direct equivalent, and some style guides vary in handling nonrestrictive elements. In general, nonrestrictive clauses provide background or incidental detail rather than defining information.