Tf-Idf

• Sparse Retrieval

  Retrieval using inverted-index term matching and scoring functions like BM25 or TF-IDF; contrasts with dense nearest-neighbour methods.

• BM25

  BM25 (Best Match 25) is a probabilistic ranking function that scores documents against a query by weighing term frequency and inverse document frequency with length normalisation.

• TF-IDF

  TF-IDF (term frequency–inverse document frequency) is a numerical statistic that reflects how important a word is to a document relative to a corpus, used as a relevance signal in search ranking.