Custom Web control is a control that inherits from web server control available in ASP.Net.
A Custom Web Control could be compiled into separate .dll file. This custom Web control can be shared across all application by installing this dll in to Global Assembly Catch.
User Control is a file (.ascx file) that contains a set of ASP.Net controls and code grouped together to provide common functionality across the application. User control can be used on different web pages of the application.
