Variables

Variables are the most frequently used operands in ColdFusion expressions. Variable values can be set and reset, and can be passed as attributes to CFML tags. Variables can be passed as parameters to functions, and can replace most constants. 
ColdFusion has several built-in variables that provide information about the server and ColdFusion tags return. For a list of the ColdFusion built-in variables, see Reserved Words and Variables in the CFML Reference.
The following two characteristics classify a variable:

• The scope of the variable, which indicates where the information is available and how long the variable persists
• The data type of the variable value, which indicates the type of information a variable represents, such as number, string, or date
  See Data types for a list of data types (which also apply to constant values). For detailed information on ColdFusion variables, including data types, scopes, and their use, see Using ColdFusion Variables.