That is boxing magazine's picture (5)
I believe the answer is:
image
'picture' is the definition.
(I know that picture can be written as image)
'that is boxing magazine's' is the wordplay.
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'boxing' means one lot of letters goes inside another ('box' can mean contain, as in to put in a box).
'magazine' becomes 'mag' (abbreviation for magazine).
'ie' placed around 'mag' is 'IMAGE'.
(Other definitions for image that I've seen before include "Photo or likeness" , "Picture; simile" , "Metaphor; figure" , "Simile, metaphor" , "Epitome" .)