Parking in French enclosure (3)
I believe the answer is:
pen
'enclosure' is the definition.
(pen is a kind of enclosure)
'parking in french' is the wordplay.
'parking' becomes 'p'.
'in french' becomes 'en' ('en' can be French for 'in' e.g. en France).
'p'+'en'='PEN'
(Other definitions for pen that I've seen before include "Write" , "See 20" , "Female swan" , "Writing implement" , "American jug?" .)