The difference between buying and selling (6,6)
I believe the answer is:
profit margin
'selling' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'the difference between buying' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'difference' could be 'margin' (margin is a kind of difference) and 'margin' is located in the answer.
This explanation may well be incorrect...
'and' acts as a link.
Can you help me to learn more?
(Other definitions for profit margin that I've seen before include "Financial gain" , "Revenue minus costs" , "what keeps firm afloat" .)