FAST Query Language (FQL) operators are keywords that specify Boolean operations or other constraints to operands. The FQL operator syntax is as follows:

[property-spec:]operator(operand [,operand]* [, parameter=”value”]*)

In the syntax:

• property-spec is an optional property specification followed by the “in” operator.
• operator is a keyword that specifies an operation to perform.
• operand is a term expression or another operator.
• parameter is the name of a value that changes the behavior of the operator.
• value is the value to use for the parameter name.

Operator names, parameter names, and parameter text values are case-insensitive. White space is allowed within the operator body, but is ignored unless it is enclosed in double quotation marks.

The length of FAST Query Language queries is limited to 2,048 characters.

Overview of FQL Operators

FQL supports the following types of operators:

Type	Description	Operators
String	Enables you to specify query operations on a string of terms. This is the most common operator to use on text terms.	STRING
Boolean	Enables you to combine terms and sub-expressions in a query.	AND, OR, ANY, ANDNOT, NOT, COUNT
Proximity	Enables you to specify the proximity of the query terms in a matching sequence of text.	NEAR, ONEAR, PHRASE, STARTS-WITH, ENDS-WITH, EQUALS
Numeric	Enables you to specify numeric conditions in the query.	RANGE, INT, FLOAT, DATETIME,
Relevance	Enables you to impact the relevance evaluation of a query.	RANK, XRANK, FILTER

For more go to the following link

http://msdn.microsoft.com/en-us/library/ff394462.aspx#fqloperator_or