The technique of overdubbing can apply to any sounds
added to a recording
at any point after the initial "live" instruments
have been tracked
to multi-track tape
It is virtually unheard of nowadays for a commercially released recording to contain no overdubs whatsoever (excepting of course most "live in concert"-type albums).
bitter_engineer: Fair point about Jazz albums. My generalisation above does fall down slightly when dealing with largely instrumental music.