Burst of activity (5)
I believe the answer is:
spurt
'burst of activity' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for spurt that I've seen before include "Gush out suddenly" , "Short spell of increased speed" , "Jet, gush" , "Gush; sudden burst" , "A short burst of activity" .)