Place is upside-down by half-term (4)
I believe the answer is:
site
'place' is the definition.
(site is a kind of place)
'is upside-down by half-term' is the wordplay.
'upside down' says the letters should be written in reverse.
'by' says to put letters next to each other.
'half-term' becomes 'te'.
'is' written backwards gives 'si'.
'si'+'te'='SITE'
(Other definitions for site that I've seen before include "Ties into building location" , "Location; locate" , "Locale" , "Position; situation" , "Building plot" .)