+ (AND)

Use before a keyword that must be included in search results. In the absence of any other operators, Google assumes that keywords are preceded by the AND operator. Example: french +fries.

- (NOT)

Use before a keyword that must be excluded from the search results. Example: soup stock -market.

' '

Use around keywords that must be matched as an exact phrase. Example: american revolution 'one if by land'.

OR

Use to match either one keyword or another. When OR is placed between two keywords, Google is forced to include one of them. Example: cheese cheddar OR swiss.