Travels in busy periods (9)
I believe the answer is:
intervals
'periods' is the definition.
(interval is a kind of period)
'travels in busy' is the wordplay.
'busy' indicates anagramming the letters.
'travels'+'in'='travelsin'
'travelsin' anagrammed gives 'INTERVALS'.
(Other definitions for intervals that I've seen before include "Intermissions" , "Rests" , "Net's viral (anag.)" , "Periods of time between parts of a play" , "Times between acts" .)