What is gpstate file in ASP.NET

In my project I found a .gpState file in the folder, What is the purpose of gpState file?

From stackoverflow

• I have never seen such a file in an ASP.NET app. Are you sure it is from ASP.NET?

  Edit: it seems this file comes form the Guidance Automation Toolkit (whatever that is).

  Sauron : I am using WCF service in my application