Definitions
1.NounA complex, troublesome situation arising when a decision or action produces considerable subsequent problems."If someone gets a promotion that might not be deserved, it could open up a whole can of worms with the other employees."
2.NounA troublesome situation; an issue whose resolution is difficult or contentious but not necessarily complex."Questioning the decision would definitely open a can of worms."
3.NounAny difficult or disgusting task, activity, topic of discussion or subject matter, which would be ideally avoided if at all possible.
4.NounUsed other than figuratively or idiomatically: see can, worm.