Postback property in asp.net

PostBack is the name given to the process of submitting an ASP.NET page to the server for processing. PostBack is done if certain credentials of the page are to be checked against some sources (such as verification of username and password using database)

Please refer below links

https://www.codeproject.com/Articles/811684/Understanding-The-Complete-Story-of-Postback-in-AS#:~:text=PostBack%20is%20the%20name%20given,username%20and%20password%20using%20database).

https://www.c-sharpcorner.com/uploadfile/2f73dd/what-is-postback-in-Asp-Net/

https://www.aspsnippets.com/Articles/AutoPostBack-property-in-ASPNet-with-examples-in-C-and-VBNet.aspx

https://www.youtube.com/watch?v=yZJQ4Z6kEzs

Please refer below links,

https://www.c-sharpcorner.com/uploadfile/2f73dd/what-is-postback-in-Asp-Net/

https://www.c-sharpcorner.com/uploadfile/37db1d/looking-deep-inside-postback-and-viewstate-in-Asp-Net-3-5/

Posting back to the page (codebehind) itself is called as postback. 

When first the request comes to any page for the first time it is not a postback, then if you do fire a click event  then it posts the control's value to the same page (samepage.aspx.cs) which is called as postback.

By Deafult only click event has postback property enabled,  to enable the Postback property of other control's you can set their postback property to true.