C#, what is the process of the var syntax and naming convention called in the following?

var answer = (radius: "The Radius is: ", circumference: "The Circumference is: ", area: "The area is: ");

Console.WriteLine(answer.radius); // Outputs: The Radius is: Console.WriteLine(answer.circumference);// Outputs: The he Circumference is: Console.WriteLine(answer.area); // Outputs: The area is: