An integral part of every assembly that renders the assembly
self-describing. The assembly manifest contains the
assembly?s metadata. The manifest establishes the assembly
identity, specifies the files that make up the assembly
implementation, specifies the types and resources that make
up the assembly, itemizes the compile-time dependencies on
other assemblies, and specifies the set of permissions
required for the assembly to run properly. This information
is used at run time to resolve references, enforce version
binding policy, and validate the integrity of loaded
assemblies. The self-describing nature of assemblies also
helps makes zero-impact install and XCOPY deployment
feasible. metadata -Information that describes every element
managed by the common language runtime: an assembly,
loadable file, type, method, and so on. This can include
information required for debugging and garbage collection,
as well as security attributes, marshaling data, extended
class and member definitions, version binding, and other
information required by the runtime.

Manifest means all the assembly meta data specifyed.
Metadata means data about data.

Manifest --> Self describing information about an assembly.
Metadata --> Content of that assembly.