Parenthetic
Parenthetic is an adjective describing material inserted into a sentence as an aside or nonessential remark, typically set off by parentheses. A parenthetic element can be a single word, a phrase, a clause, or an entire sentence that adds information or a caveat but is not required for the main argument to be understood.
Origin: The term comes from the Greek parenthesis meaning “placing beside,” via Latin and French into English.
Usage and examples: In prose, parenthetic material clarifies or adds color without forcing the reader to accept
Stylistic notes: The term parenthetic is somewhat formal; many editors and guides favor the noun-adjective pair