There's not much flesh on this small, trim guy (5,3)
I believe the answer is:
spare rib
'there's not much flesh' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'this small trim guy' is the wordplay.
'this small' becomes 's' (abbreviation - e.g. clothes size).
'trim' becomes 'pare' (synonyms).
'guy' becomes 'rib' (both can mean to tease).
's'+'pare'+'rib'='SPARE-RIB'
'on' is the link.
Can you help me to learn more?
(Other definitions for spare rib that I've seen before include "Only a little pork on this bone" , "God gave Adam" , "piece of pork" , "cut of meat" , "Bone in barbecue sauce, say" .)