What is an UpdatePanel Control?

An UpdatePanel control is a holder for server side controls that need to be partial postbacked in an ajax cycle. All controls residing inside the UpdatePanel will be partial postbacked. Below is a small example of using an UpdatePanel.
As you see here after running the snippet above, there wont be a full postback exhibited by the web page. Upon clicking the button, the postback shall be partial. This means that contents outside the UpdatePanel wont be posted back to the web server. Only the contents within the UpdatePanel are refreshed.