Restricting the matches made during a computer search by adding other criteria to the search terms. If you were searching for materials on physics, you could limit yourself to only books published after 1980. This would be limiting by format and by date.
Database feature that allows you to search for words that occur in a particular field (or part) of the database record (such as the URL, title, subject heading, etc.) or to narrow search results by some other criteria (domain, geography, language, etc.).