noun (n)

• either of two punctuation marks (or) used to enclose textual material(noun.communication)

  source: wordnet30
• a message that departs from the main subject(noun.communication)

  Synonym:
  aside, digression, divagation, excursus
  

  source: wordnet30
• A word, phrase, or sentence, by way of comment or explanation, inserted in, or attached to, a sentence which would be grammatically complete without it. It is usually inclosed within curved lines (see def. 2 below), or dashes.(noun)

  source: webster1913