Product attributes are additional pieces of information that are associated with a product (see @4.5. Product attributes for more information). If you want to have attributes included within the keyword search, ensure you check the 'Include in search' checkbox for the attribute in the back end. For example, a book store might have ISBN, Author and Publisher as attributes which you'd probably want to include in the search. Electrical items on the other hand might have voltage and power requirement values in numbers - you'd probably not want to include these in the search as numbers are unlikely to generate direct matches to help search results.