Post Office stocks exciting picture (5)
I believe the answer is:
photo
'picture' is the definition.
(photo is a kind of picture)
'post office stocks exciting' is the wordplay.
'post office' becomes 'po'.
'stocks' indicates putting letters inside (stocks can mean carries or contains).
'exciting' becomes 'hot' ('hot' can be similar in meaning to 'exciting').
'po' going around 'hot' is 'PHOTO'.
(Other definitions for photo that I've seen before include "Picture, in short" , "Snap, exposure, in short" , "Snap - shot" , "Pic (abbr)" , "Snap, picture" .)