noun
parenthetical expression
Linguistics term for a word, phrase, or clause inserted into a sentence as an aside, often marked by parentheses, commas, or dashes.
「彼は、そうにゅうくを使いながら、話を続けた。」
He continued talking, using parenthetical expressions.
この文のそうにゅうくは、補足情報を提供して
The parenthetical expression in this sentence provides supplementary information.
句 means 'phrase' or 'clause'; 挿入句 is a compound meaning 'inserted phrase'.
Compound of 挿入 (insertion) + 句 (phrase/clause). The exact historical derivation is uncertain, but the term follows standard Sino-Japanese word formation patterns.