Space friend 

Shortened version of boy friend or girl friend (not to be confused with boyfriend/girlfriend). The origin comes from saying "boy space friend or girl space friend" so as not to be confused with a significant other. Basically, the definition of friend zoned.
The absolute closest person in the world to you. Someone you have told all of your secrets to and aren't uncomfortable in any way, shape, or form when with them. They are closer than a best friend, a sibling, and even a significant other.

John: Hey, is that your boyfriend
Laura: No, that's my space friend

Space friend by Rubikscuber April 20, 2015

girl space friend 

A girl who is a friend but NOT a girlfriend (one that's actually in a relationship) and often implied to be one.

May or not be a "friend with benefits"

Jason: Hey is Jake actually seeing Katie?

Cole: Naw, she's just his girl space friend.

girl space friend by Sensi the Sensei January 29, 2010

spare tyre friend 

A friend who is primarily used as a backup wen other, more entertaining options go awry or are simply unavailable. The "side dip" of the friendship list. The "Wii" when the other more entertaining friends Xbox and PS3 have been broken through excessive use. The "spare tyre", the one you were hoping not to use.

1. When a friend,lets call him Jack, only starts talking to you at a late hour, lets say 01:25. But at no other time...YOU are the spare tyre friend

spare tyre friend by sparetyrefriend January 18, 2011