Communication system Number Ten backed (8)
I believe the answer is:
ethernet
'communication system' is the definition.
(I've seen this before)
'number ten backed' is the wordplay.
'number' becomes 'ether' (I've seen this before).
'backed' shows that the letters should be reversed in order.
'ten' back-to-front is 'net'.
'ether'+'net'='ETHERNET'
(Other definitions for ethernet that I've seen before include "food" , "Communication system" , "Local area computer network" , "comms system" , "System connecting several computers" .)