Form of meat loaf maybe containing a lump of fat (5)
I believe the answer is:
offal
'form of meat' is the definition.
'offal' can be an answer for 'meat' (offal is a kind of meat). I am not certain of the 'form of' bit.
'loaf maybe containing a lump of fat' is the wordplay.
'maybe' indicates an anagram.
'containing' indicates putting letters inside.
'a lump of fat' becomes 'f' (I can't justify this - if you can you should believe this answer much more).
'loaf' is an anagram of 'ofal'.
'ofal' placed around 'f' is 'OFFAL'.
Can you help me to learn more?
(Other definitions for offal that I've seen before include "Entrails/organs as food" , "Less valuable edible parts of animal" , "Edible (or inedible?) internal organs" , "Waste matter" , "Meat product" .)