Assembly manifest contains the detail of assembly i.e.Assembly name,version number,culture,strong name information ,list of file in assembly ,type referance information but Metadata Metadata describes all classes and class members that are defined in the assembly, and the classes and class members that the current assembly will call from another assembly. The metadata for a method contains the complete description of the method, including the class (and the assembly that contains the class), the return type and all of the method parameters.Metadata describes all classes and class members that are defined in the assembly, and the classes and class members that the current assembly will call from another assembly. The metadata for a method contains the complete description of the method, including the class (and the assembly that contains the class), the return type and all of the method parameters.

in simple language assebly can contain multiple module each module have its metadata but single manifest for assembly . manifest contains info about assembly overall what r the modules it contains further metadata describes module .