1. a predisposition to admire all of a person's actions, work, etc., because of an estimable quality or action in the past.
2. Psychol.a potential inaccuracy in observation, as of a person, due to overgeneralization from a limited amount of evidence or the influence of preconceived beliefs or a priori hypotheses: The assumption that he is an authority on the subject is a halo effect of his Ivy League manner.
3. any desirable side effect.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.