Best selling YA author Maggie Stiefvater (Shiver, Lament) writes about Plot Bunnies in her blog here.
Plot Bunnies are the ideas that hop along while you're in the middle of your novel and beguile you away, like fluffy sirens, from the your current work-in-progress.
Beware the Bunnies of Plot! Note my earlier post about staying on target. It's easy to follow these seemingly innocent creatures in their waistcoats muttering about how they're late for a very important date. But then you fall down a rabbit hole. You just might never get back to your work-in-progress. Now that you're in the middle of the darn thing, it doesn't look quite as soft and sweet and adorable as the Plot Bunny. It doesn't tempt you with all its promise of being the Best Idea Ever any more. Now, it's work.
Well, you have to do the work if it's ever gonna grow up and be a Real Novel.
So, write down your Plot Bunnies, then put them away. They'll stay in your drawer, grousing slightly but quiescent. Once you're done with your WIP, then you can pull them out, dust them off, and follow one off your next adventure.