Pitch shifting
Moving a sound up or down in pitch without making it shorter or longer at the same time.
A tape machine can only do both at once: speed it up and the pitch rises, slow it down and it drops. Digital processing splits the problem in two. Either the audio is time-stretched first and then resampled back to its original length, or the frequencies are moved directly in a phase vocoder. Speech and vocals often get PSOLA instead, which cuts out individual pitch periods and packs them closer together or further apart.
The Eventide H910 of 1975 was the first commercial digital box for the job and lent its name to the whole harmonizer category. The classic trap is formants: shift them along with the pitch and a voice a fifth up turns into a chipmunk. Modern algorithms hold them in place, which is the difference between a corrected vocal and a cartoon.