1. A method for statistically extracting terms from a set of documents comprising the steps of: determining for each document in the set of documents an importance vector based on importance values for words in each document; forming a binary document classification tree by clustering the documents into clusters of similar documents based on the importance vector for each of the documents; building an infrastructure for the set of documents by generalizing the binary document classification tree; clustering the documents by cutting the generalized tree of the infrastructure; extracting statistically significant individual key words from the clusters of similar documents; and extracting terms using the key words as seeds.