An array is a data structure consisting of a group of elements that are accessed by indexing. In most programming languages each element has the same data type. However, ColdFusion, as we will see, is not strictly typed and therefore allows any data type to be stored in combination. This allows strings, integers, booleans and other complex data types all to be stored in the same array. However, doing this certainly isn't a good practice as it causes signification complication when accessing the stored data.
Variables of a simple data type commonly only store a single value but, in some situations, it is useful to have a variable that can store a series of related values - using an array. Arrays are described as complex data types because they can hold data in a structured, complex way. Read more – ‘Implicit Arrays in ColdFusion 8’.