A reference type is a class type, an interface type, an array type, or a delegate type. reference-type : class-typeinterface-typearray-typedelegate-typeclass-type : type-nameobjectstringinterface-type : type-namearray-type : non-array-typerank-specifiersnon-array-type : typerank-specifiers : rank-specifierrank-specifiersrank-specifierrank-specifier : [dim-separators]dim-separators : ,dim-separators,delegate-type : type-name A reference type value is a reference to an instance of the type, the latter known as an object. The special value null is compatible with all reference types and indicates the absence of an instance.