In software engineering the concept of abstraction is extremely important. Microsoft calls its own language abstraction layer the Common Intermediate Language (CIL). Similar to byte code like Java generates IL supports all object oriented features including data abstraction, inheritance, polymorphism, etc. In addition to these features IL supports other concepts such as properties, fields and enumeration. Any .net language can be converted into IL, so .net supports multiple languages and perhaps multiple platforms. CIL is also called as MSIL (Microsoft Intermediate Language). When .net code is compiled it is converted into IL, which is then executed. Because of IL objects created in one language can be accessed and derived from another. E.g. it is possible to create a class in VB.Net and derive from it in C#.

Enumeration and Iterator both are using looping statement.Enumeration is legacy class.iterator is cotains extra
method than Enumeration.
Enumeration is a read only interface, by using this we can loop thro' the elements only. But using iterator interface we can traverse and also remove the object.

Vector and ArrayList are very similar. Both of them represent a 'growable array', where you access to the elements in it through an index.
ArrayList it's part of the Java Collection Framework, and has been added with version 1.2, while Vector it's an object that is present since the first version of the JDK. Vector, anyway, has been retrofitted to implement the List interface.
The main difference is that Vector it's a synchronized object, while ArrayList it's not.
While the iterator that are returned by both classes are fail-fast (they cleanly thrown a ConcurrentModificationException when the orignal object has been modified), the Enumeration returned by Vector are not.
Unless you have strong reason to use a Vector, the suggestion is to use the ArrayList