Grey Sheep

# Dictionary
A person who poses as one of an "outsider" clique in order to feel belonging or fill a social void. Does not refer to any one clique, covers a large spectrum.

This term is derived from black sheep, whereas that term generally refers to someone who is an individualist, grey sheep applies to someone who is conforming to fit in.

Person A: "Dude, Josh started wearing all black and hasn't talked to me much. Is something wrong with him?"
Person B: "No, look at his fancy new clique. He's just being a grey sheep."

(http://www.urbandictionary.com/define.php?term=Grey+Sheep)


# In Collaborative Filtering 
Grey sheep refers to the users whose opinions do not consistently agree or disagree with any group of people and thus do not benefit from collaborative filtering.

(Xiaoyuan Su and Taghi M. Khoshgoftaar, A survey of collaborative filtering techniques, Journal Advances in Artificial Intelligence archive Volume 2009)