So far, we have seen Solr searching by the keyword used in search query. Result clustering is the advanced search component of Solr; it first identifies the similarities between documents, and using these similarities, it finds related documents. It is also not necessary for the identified similarities to be present in the query or document.

The clustering component first discovers the results of a search query and identifies similar terms or phrases found within the search results. A clustering algorithm discovers relationships across all the documents from the search result and forms in a meaningful cluster label. Solr comes with several algorithms for clustering implementation.