Lucene is an open source search engine, originally implemented in Java by Doug Cutting distributed under Apache Software License. Lucene is currently available in programming languages including Perl, C#, C++, Python, Ruby and PHP.
Main applications of Lucene include
Full text indexing and searching capability.
Internet search engines, single-site searching.
Lucene's logical architecture takes document as a container of fields of text. Hence file format is unimportant for the Lucene.
This is just an introduction, We will have lot of arguements coming here relating to this topic in this category