A boondoggle is a useless, trivial piece of work — it's a waste of time. If you're serious about your career, you should avoid boondoggles.
Boondoggle is a silly sounding word for a silly project. Any endeavor that's a total waste of time or has no value could be called a boondoggle, especially if you're doing it just to look busy and important. The verb boondoggle means to do that useless work. If the mayor spends all his time promoting an eagle reserve in the middle of the Bronx instead of focusing on subway repairs, you could call that a boondoggle.