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: