This page lists short explanations of special terms regarding regain and search engines.

When the crawler found a document and extracted the text, then it stores that text in the search index using Lucene.

Lucene extract every single word from the document's text. Before the words are stored in the index, they are reduced to their base form using an analyzer. So searching for tree and trees has the same results.

The syntax of search queries.

Details see http://jakarta.apache.org/lucene/docs/queryparsersyntax.html

Stopwords are words that shouldn't be stored in the index.