The words are supposed to be there but have been left due to any reason. Is there a succinct term to describe such words?
There's some disagreement going on here that can be attributed to differing interpretations of the question.
If the text was once there but is now missing or illegible, it is a lacuna.
If a word or phrase was left out unintentionally, it is an omission or elision.
If a word or passage has been intentionally removed, it is a redaction.
A caret mark (^) used to note an omission but generally where something is to be inserted. An eclipsis denotes "omission or suppression of parts of words or sentences [syn: ellipsis]". Note: 'caret' is Latin for missing
Haplography n. - accidental omission of letters, words or lines in copying
Interesting that this sticks: