A UserStory that is TooBig, per UserStoriesApplied by MichaelCohn
Some big stories require monolithic technical achievements, such as "hide a mountain" (DouglasAdams), or BoilTheOcean (WillRogers). These should be reduced to incremental feats, such as "hide a rock" or "boil a frog".
Some require too many complex technical details that should be teased apart. See TheAlmightyThud.
What's the relationship or distinction between an EpicUserStory and a MotherhoodStory?