Stop words are common words like "the," "is," "in," and "and," which are often ignored by search engines when processing queries. These words are considered to have little value in helping identify the meaning of a search because they appear frequently across most documents and don't contribute significantly to the query's relevance.
Search engines generally exclude stop words from indexing and searching, aiming to focus on more meaningful words that help define a user's intent. By removing stop words, search engines improve both the efficiency and accuracy of their retrieval processes.
However, in certain cases, search engines may include stop words if they are essential to the meaning of the query. For instance, in a query like "What is the best way to cook rice?" excluding "the" could change the meaning of the search. Some search engines also allow users to search for exact phrases, including stop words, if needed.