Inverting is a means of hiding weaves of the One Power. An inverted weave is thought to be invisible to anyone except the person who originally wove it.
Moghedien, while trapped and collared by the a'dam, teaches Elayne and Nynaeve how to invert their weaves. They teach Egwene who in turn teaches the rest of the Aes Sedai in Salidar. Cadsuane had learned inversion sometime before the Battle near Shadar Logoth.