sexのようなどんな単語でも探してください。
 
1.
A person who is a friend, only when your other friends are not present.

Also referred to as a "number two". Any social networking site has a Top Friends, and the number is your next best friend.
"Well, John isn't here, so I guess I'll have to talk to my fill-in friend."

"Amy had to go to the concert, so I guess it's just me and the number two."
NOT a fill-in friend.によって 2009年05月03日(日)

Words related to fill-in friend

2 conditional-friend fillin friend number 2 number two