Web parts are the new building blocks of personalization in ASP.NET 2.0. Any controlwhether a standard server control, custom control, user control, or web part controlcan be used as a web part without modification.
In its simplest form, a web part consists of an ASP.NET server or user control that takes advantage of the Web Parts control set, which is a group of structural components consisting of the following minimum set:
Responsible for managing all other web part controls on the page
Defines an area on a page where web parts can be placed
Responsible for managing the user interface that displays the available web parts and provides the user the ability to select web parts and add them to WebPartZones