In some songs, a line in one verse will be a syllable longer than the matching line in other verses, and this will be resolved by adding an extra note to the start or end of that line of melody (in that verse), making the line longer by cutting into the time between lines.
The first example that comes to mind is Queen's Death On Two Legs, which has this on almost every line in the last verse.
What is this called?
Something similar also happens commonly in hymns. The extra syllable is added by splitting (e.g.) a minim into two crotchets, adding the extra note without lengthening the line. I'm not specifically asking about this, but maybe it is covered by the same name.