Many songs have "minor" phrases added in - either officially or in common practice - at the ends of lines, which comment on the lyrics but can be left out without affecting the lyrics' meaning.
For example, when people sing "Rudolph the Red-Nosed Reindeer", at the end of the line "had a very shiny nose" they often add "(like a light bulb!)".
These seem especially common in rap songs, where they are usually very short and written in parentheses in the written lyrics. For example, in 50 Cent's "In Da Club", at the end of the line "Been hit with a few shells, but I don't walk with a limp" he adds a quick "(I'm aight)".
Is there a term for these minor/optional and short "additional, background" lyrics?