Meaning of shaggy-dog story

shag'gy-dog' sto"ry

Pronunciation: (shag'ē-dôg', -dog'), [key]
  1. a funny story, traditionally about a talking dog, that, after an often long and involved narration of unimportant incidents, has an absurd or irrelevant punch line.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.