It's official: "Friend zone" is a word. 

Here's how Oxford Dictionaries defines “friend zone," via:

“a situation in which a platonic relationship exists between two people, one of whom has an undeclared romantic or sexual interest in the other: I always wind up in the friend zone, watching them pursue other guys“

In related news, anyone who looks up "friend zone" in a Oxford Dictionary is probably stuck in it for life. 

[H/T: COED]