Officers are in the commercial enterprise with 51 outside listings (8)
I believe the answer is:
colonels
'officers are in the commercial' is the definition.
'colonels' can be an answer for 'officers' (I've seen this before). I'm unsure of the 'are in the commercial' bit.
'enterprise with 51 outside listings' is the wordplay.
'enterprise' becomes 'co' (company).
'with' is a charade indicator (letters next to each other).
'5l' becomes 'lone' (I can't justify this - if you can you should give a lot more credence to this answer).
'outside' means to remove the middle letters (I've seen 'outside of' mean this).
'listings' with its centre removed is 'ls'.
'co'+'lone'+'ls'='COLONELS'
Can you help me to learn more?
(Other definitions for colonels that I've seen before include "Military personnel" , "Senior military officers" .)