Briefly explain what user controls are and what server controls are and the differences between the two.
An ASP.NET control (sometimes known as a server control) is a server-side component that is shipped with .NET Framework. A server control is a compiled DLL file and can't be edited. It can, however, be manipulated by its public properties at design-time or runtime. It is possible to build a custom server control (sometimes known as a custom control or composite control).