Using advanced search - Gmail Help

Some new and useful options for searching Gmail content (see the full page for search operators and examples)

"Advanced search operators are query words or symbols that perform special actions in Gmail search. These operators allow you to find what you're looking for quickly and accurately. They can also be used to set up filters so you can organize your inbox automatically. Some of the most useful operators are listed below.
You can also refine your search by clicking the arrow in the search box."

Using advanced search - Gmail Help