Note: the content of this post is mainly notes taken from professor Stefano Mizzaro’s lessons on (Web) Information Retrieval at Uniud.
These terms are used in different topics of IR and it is useful to define them before diving specifically into a topic:
N: number of documents in the collection
Index term: if the term is in the index
t: number of terms in the index
ki: keyword, a term in the index
K: set of keywords
wi,j: weight of ki in dj