A hash is an un-ordered group of KEY-VALUE pairs and keys are unique strings(duplication of keys are not allowed). The values are scalar and they can be either a number ,a string or a reference. These are also called as associative arrays.
Before using the hash we have to first declare it
As I said above duplication of keys are not allowed and this property can be used to list out the elements without any repetition. Let us consider a array of numbers with repetition.