r digital object and the means of providing access to it, normally in a wrapper that describes what it is in a way that can be understood by a wide range of technologies (such as an XML document). [Computer and Information Sciences] 
n., The technique used by layered protocols in which a layer adds header information to the protocol data unit (PDU) from the layer above. As an example, in Internet terminology, a packet would contain a header from the physical layer, followed by a header from the network laye