Addition. The word interlined designates one of the most common forms of addition, an inscription made above (or when specified as such, below) the usual line of writing. (An editor could include above in the description, but in most instances doing so would be unlikely to add to the commonly perceived sense of the participle alone.) A related term, inserted, when used by itself means that new characters or words have been added within an existing line (as evidenced by spacing, the shapes of the letterforms, the nature of the ink or lead, and similar characteristics); it may also be combined with descriptive phrases to identify other additions that are not interlineations (as in: inserted in left margin).
(Meulen et al. 1999, 206)