 <p>Per this <a href="http://www.liferay.com/web/guest/community/wiki/-/wiki/Main/Pluggable+Enterprise+Search+with+Solr" rel="nofollow">link</a> it is to externalize the search function from the portal. </p> <p>Using Solr instead of Lucene gives you the additional capabilities of Solr such as Replication, Sharding, Result clustering through Carrot2, Use of custom Analyzers/Stemmers etc. </p> <p>It also can offload search server processing to a separate cluster.</p> <p>Opens up the possibilities of search driven UI (facetted classification etc) separate from your portal UI.</p>