1. Stemming and stop words elimination is done in traditional IR systems, and is not used now.
2. Inverted index is a data structure which maps the documents to terms. i.e it says which document conatain which term
3. All the terms in the index is reffered to as Lexicon or Vocabulary
4. Position information of a term in a document is useful for Proximity queries and also while displaying the snippet
-Bharath
