The fuller name, Okapi BM25, includes the name of the first system to use it, which was the Okapi information retrieval system, implemented at London's City University in the 1980s and 1990s.
Okapi BM25 is a comprehensive designation that includes the name of the first system to employ it, namely the Okapi information retrieval system, introduced at London's City University during the 1980s and 1990s.