Search operators (sometimes called advanced operators or search parameters) are special characters, strings of characters, or commands that narrow down the focus of an online search. In computer science, “operators” are characters or combinations of characters that people use to represent an action or cause an action to occur.
Basic search operators include putting the query in quotation marks to search for the exact phrase and using a minus (-) sign before terms you want to exclude. By using advanced search operators, users can search by websites, file type, and characters in URLs. There are hundreds of search operators that enable specific searches. It is possible to combine search operators on a single search. There are almost limitless combinations available.
A good list of many of the search operators available can be found at the SearchEngineJournal.