field day

Short definition from Wiktionary

Noun

1. 1
   A day for maneuvers and tactical exercises in the field (across the landscape).
2. 2
   A school day for athletic events.
3. 3
   A day of class taken away from school for a field trip.
4. 4
   A great time or a great deal to do; a period of bustling activity.
5. 5
   A great time or a great deal to do, at somebody else's expense.
6. 6
   A day on which there is top-to-bottom all-hands cleaning.