IsPostBack is a property of the Page that tells you whether or not the page is on its inital load or if a user has pressed a button on your WebForm that has caused the page to post back to itself.
General use is normally something like:
//do something only the first time the page is loaded
This MSDN document will give you a better explination of this and the Page Lifecycle as a whole:
Read this if you want to know how to get a correct reply for your question:
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