A type fully describes a value if it unambiguously defines the value's representation and the operations defined on that value.
For a value type, defining the representation entails describing the sequence of bits that make up the value's representation. For a reference type, defining the representation entails describing the location and the sequence of bits that make up the value's representation.
A method describes an operation that can be performed on values of an exact type. Defining the set of operations allowed on values of an exact type entails specifying named methods for each operation.
Some types are only a partial description; for example, interface types. These types describe a subset of the operations and none of the representation, and hence, cannot be an exact type of any value. Hence, while a value has only one exact type, it can also be a value of many other types as well. Furthermore, since the exact type fully describes the value, it also fully specifies all of the other types that a value of the exact type can have.
While it is true that every value has an exact type, it is not always possible to determine the exact type by inspecting the representation of the value. In particular, it is never possible to determine the exact type of a value of a value type. Consider two of the built-in value types, 32-bit signed and unsigned integers. While each type is a full specification of their respective values (i.e., an exact type) there is no way to derive that exact type from a value's particular 32-bit sequence.
For some values, called objects, it is always possible to determine the exact type from the value. Exact types of objects are also called object types. Objects are values of reference types, but not all reference types describe objects. Consider a value that is a pointer to a 32-bit integer, a kind of reference type. There is no way to discover the type of the value by examining the pointer bits; hence it is not an object. Now consider the built-in CTS reference type System.String (see Partition IV). The exact type of a value of this type is always determinable by examining the value, hence values of type System.String are objects, and System.String is an object type.