Chorusing does a similar operation as the harmonizing yet the frequencies are shifted by +/- the fundamental. This give the signals the effect that multiple sounds are being played in unison and there pitch is just slightly off. My interpretation chorusing is very weak but a simple chorusing effect is nonetheless accomplished.

Signal Comparison (please click on the graphic)

M Files:
Example
chorus.m

Wave File Examples:
Wave File 1 - Chorus
Wave File 2 - Chorus