Fly places to fill time on vacation
I believe the answer is:
tse-tse
'fly' is the definition.
(I have seen 'African fly ' mean 'tse-tse' so perhaps 'fly' could also mean 'tse-tse')
'places to fill time on vacation' is the wordplay.
'places' becomes 'sets' (setting is a kind of placing**).
'to fill' is an insertion indicator.
'on vacation' suggests removing the centre.
'time' with its middle taken out is 'te'.
'sets' inserted inside 'te' is 'TSE-TSE'.
(Other definitions for tse-tse that I've seen before include "African fly that transmits sleeping sickness" , "Central African fly" , "Disease-carrying fly" , "The biting fly causing sleeping sickness" , "This fly carries sleeping sickness" .)