What is punch-in?
Recording over a specific section of an existing take without re-recording the whole track. The singer needs a couple of lines of lead-in to match the energy and phrasing of the surrounding material.
This is where a prompter earns its place quietly: seeing the lines before the punch point is what makes the repair match instead of sounding pasted in.
Building one final vocal from the best parts of several takes. The editor chooses per line or per phrase and crossfades between them, which is far quicker when every take was sung with consistent phrasing.
Stacked rows holding multiple recorded takes on one track, letting you audition and select between them. Most modern DAWs create them automatically when you record over an existing region.