title: Difference between feature selection, feature extraction, feature weights
body: <p>I am slightly confused as to what "feature selection / extractor / weights" mean and the difference between them. As I read the literature sometimes I feel lost as I find the term used quite loosely, my primary concerns are -- </p>
  
  <ol>
  <li><p>When people talk of Feature Frequency, Feature Presence - is it feature selection?</p></li>
  <li><p>When people talk of algorithms such as Information Gain, Maximum Entropy - is it still feature selection. </p></li>
  <li><p>If I train the classifier - with a feature set that asks the classifier to note the position of a word within a document as an example - would one still call this feature selection?</p></li>
  </ol>
  
  <p>Thanks
  Rahul Dighe</p>