Class variables compared with instance variables

Two objects from the same class usually hold different values. Occasionally you want a value that all of them share. The difference is one keyword.

Per object, the default

A normal field belongs to each object separately. Change it on one object and the others are untouched.

Per class, when shared

A static field belongs to the class itself. Every object sees the same value, and it exists even before any object is created.

public class Visitor
{
    public string Name;            // per object
    public static int Total;      // shared by all
}

To keep many classes tidy, you group them into namespaces.