ID American men are using (8)
I believe the answer is:
username
'id' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'american men are using' is the wordplay.
'american' becomes 'us' (abbreviation for United States).
'using' indicates anagramming the letters.
'men'+'are'='menare'
'menare' anagrammed gives 'ername'.
'us'+'ername'='USERNAME'
Can you help me to learn more?
(Other definitions for username that I've seen before include "Log in identifier" , "One's identifier on a computer" , "Online identity" , "Electronic identity" , "Person's computer ID" .)