trick' or treat'
a children's Halloween custom, in which they call on neighbors, using this phrase, and threaten to play a trick if a treat is not given.
trick-or-treatPronunciation: (trik'ur-trēt'), [key]
to become involved or take part in trick or treat.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.