parenthetical

Short definition from Wiktionary

Adjective

1. 1
   using, containing, or within parenthesis
2. 2
   that explains or qualifies something
3. 3
   that is incidental

Noun

1. 1
   A word or phrase within parentheses.
2. 2
   A descriptor or modifier enclosed within parentheses and put, indented, in a line of dialogue to describe how it should be acted or directed onscreen.