Array and Structures are considered to be complex data types in ColdFusion. In contrast, simple data types are ones that contain a single piece of data, such as an Integer, String, or Boolean value. A complex data type can contain multiple pieces of data, which, in the case of arrays, are usually related. All the data are referenced under a single variable name. You can think of a complex variable as a variable that contains a collection of other variables inside it. An array maps Integers to arbitrarily typed objects (Integers, Strings, Booleans and Objects) while a structure, or associative array, maps arbitrarily typed objects to arbitrarily typed objects. Read more – ‘The Inner Workings of a ColdFusion Array and Structure’.