Static Fields

They are also known as class static fields, static class variables or static member data.
These are useful when you want to define a value that applies to all objects of a given type.
Often used to keep a count of the number of objects that have been instantiated.
Often used to store a value that must be shared amoing all the instances.

public class Animal 
{ 
   private int _Age; 
   private static int _Count; 
} 
class Program 
{ 
   static void Main(string[] args) 
   { 
      Animal mydog = new Animal(); 
      Animal mycat = new Animal(); 
      mydog.Age = 2; 
      Animal._Count += 1; 
      System.Console.WriteLine(Animal.Total); 

      mycat.Name = "two"; 
      Animal._Count += 1; 
      System.Console.WriteLine(Animal.Total); 

      System.Console.ReadLine(); 
   } 
} 

Static Constructor

A static constructor allows you to control the initialisation of static variables.
A static constructtor will be called before a class is used.