ASP.NET offers many server controls like button, textbox, DropDownList etc. Each control can respond to the user's actions using events and event handler mechanism.
There are three types of server control events:
Postback events
This events sends the web page to the server for processing. Web page sends data back to the same page on the server.
Cached events
These events are processed when a postback event occurs.
Validation events
These events occur just before a page is posted back to the server.