A Glamour is a spell cast by a sorceress that causes the person she casts it over to become temporarily infatuated with her. It is seen as the moral equivalent of rape. Casting a glamour is seen as such a crime by the Sisters of the Light that it is punishable by death.
Someone who has had a glamour cast over them, will dedicate themselves to the sorceress who did the casting, to the exclusion of all others.
Valdora was a well known case among the Sisters of the Light of someone who abused their powers by ensnaring the minds of men and relishing the attention. She was warned on several occasions to stop what she was doing, however in the end she was tried by the Sisters and it was only the intervention of Prelate Annalina that kept her from the death penalty. Instead she was banished from the Palace of the Prophets.
Lunetta Brogan would also cast it on Tobias from time to time (although apparently with his consent), in order to engage in incest. She also cast it upon Cathryn Lumholtz, in order to make her irresistibly attractive to Richard Rahl. This was done because Tobias wanted Cathryn to get close to Richard to kill him.