For any given language or topic, stop-words are typically short words that occur frequently in texts.
They are found in most documents and thus do not provide much value in terms of saying which result should be scored higher than another.
As such, it can be a good idea to remove them from queries improve scoring.
The search string is split, by unicode boundaries, into words. Each word matching a stop word is then removed from the search string.
This all happens before the synonyms stage.
You can have multiple stop-word lists and use them in various combinations via interfaces.
|Be careful when adding stop words, it may quickly lead to an empty search string and no search results.