Relevance Feedback techniques tend to focus on one of two emphases:
In this paper, term weighting will refer to techniques that weight one term differently from another. A related concept is relative term weighting. Relative term weighting is a technique whereby older terms as a whole are weighted differently than newer terms.
Term selection will refer to techniques that select which candidate terms, all of which have a non-zero weight associated with them, are added or deleted from the query. Typically, term selection is implemented by using a term ranking formula to sort all candidate terms, and then selecting a set number of top candidates. In the literature, this implementation is often referred to as using alternate sorts for term selection.