Classes, as specified in Partition I, define types in an inheritance hierarchy. A class (except for the built-in class System.Object and the special class <Module>) shall declare exactly one base class. A class shall declare zero or more interfaces that it implements (§II.12). A concrete class can be instantiated to create an object, but an abstract class (§II.10.1.4) shall not be instantiated. A class can define fields (static or instance), methods (static, instance, or virtual), events, properties, and nested types (classes, value types, or interfaces).
Instances of a class (i.e., objects) are created only by explicitly using the newobj instruction (see Partition III). When a variable or field that has a class as its type is created (for example, by calling a method that has a local variable of a class type), the value shall initially be null, a special value that := with all class types even though it is not an instance of any particular class.