Curses are effects - either magical or divine - that sap abilities, place restrictions on a person, and generally do malevolent things. They range from the most simple of curses, which tend to restrict combat abilities, to the most complex and powerful curses. More exotic curses do not affect a person's abilities. Rather, they specify contingencies that affect the victim if certain conditions are met.
Curses used in combat tend to be of a divine nature, and slow, befuddle, or confuse enemies. They are typically short-lived, and wear off on their own with no other ill effects.
Certain curses live on into legend, either because of their efficacy, or because of their subjects, or both. The most famous example is the curse bestowed upon Erika Redmark by Garzahd. The curse would kill her if she ever came in contact with sunlight, and was fulfilled in her battle with Rentar-Ihrno, when her opponent blasted a hole in the ceiling, killing Erika instantly.