You are probably talking about Cosine similarity ( http://en.wikipedia.org/wiki/Cosine_similarity http://en.wikipedia.org/wiki/Cosine_similarity ) , a commonly

You are probably talking about Cosine similarity ( http://en.wikipedia.org/wiki/Cosine_similarity http://en.wikipedia.org/wiki/Cosine_similarity ) , a commonly used technique in the field of IR/NLP.