A couple that is so intertwined with each other's life that they never do anything without the other present. They act as if being torn apart from each other would cause physical damage to themselves such as with the Schistosoma parasite where the female is literally intertwined within the male.

Noun: a friend who is usually only called upon by a friend when a more primary/prominent friend is unavailable.

Taken from the term “second string” in an athletic competition situation. In football, if the star quarterback gets injured during a play, the second string is called off the bench to replace him/her. A “Second String Friend” is essentially benched until needed, if ever.

Synonyms: Plan B, Second Choice, Secondary Friend, Benched Until Needed