Glamour is the ability to disguise oneself as someone else. Like in "House Call" Paige made herself look like Glen's fiance. In "Y tu Mummy Tambien" or, "The Mummy's Tomb" Leo disguised himself as the demon. I can't remember what the name of the episode, but when Prue was alive, Leo glamoured into Belthazor so they could practice. Hope that answers your question!
