(no operator)
Stand alone words are optional in the results.

+
indicates that a word must be present in the results.

-
indicates that a word must not be present in any of the results.

>
indicates that a word is more important to the results

<
indicates that a word is less important to the results

( )
indicate a group of words as subexpressions and may be nested.

˜
indicates that a word is a noise word and will lower the ranking of results that contain it.

*
The asterisk can be used to truncate words as a kind of wildcard character.

"
A phrase that is enclosed in quotes returns only results that contain that exact phrase.