generally an enemurator is type that can be sorted, less commonly it is used as Enum which is when you want a list of constants that have names. The I prefix means it is an Interface.

an example would be a List(Of Integer) this list could have random numbers added to it and then sorted into numerical order.

Almost any array is Enumerable and most Lists are

Enumeration also allows items within the structure (be it a list or an array or an IEnumerable or whatever enumerable) to be searched.