Employment centre in busy period (5)
I believe the answer is:
usage
'employment' is the definition.
('usage' can be a synonym of 'employment')
'centre in busy period' is the wordplay.
'centre in' means to look at the middle letters.
'period' becomes 'age' (I've seen this before).
The middle letters of 'busy' are 'us'.
'us'+'age'='USAGE'
(Other definitions for usage that I've seen before include "Way of treating" , "Habitual custom" , "Utilisation" , "Way of employing" , "Customary way in which language is spoken or written" .)