METS is an XML schema allowing users to "wrap" existing descriptive metadata in any format with structural, technical, administrative, preservation, and meta-metadata to create a single metadata object for a resource. METS provides extension schemas with recommended technical metadata for still images, audio, and video.
METS is designed specifically for digital library objects, emphasizing
the inclusion of appropriate structural and administrative/technical
metadata, which would not ordinarily be needed for description of a
Descriptive metadata may be stored in the METS document, but it can
also just be a reference to records in other formats (MARC, EAD, etc.)
Likewise, administrative metadata can be internal or external.
METS is a very detailed format, and can contain an incredible amount
of information. It can include information about copyrights. It can
also include a description of the master file and all files that were
derived from it.
If you're familiar with Variations2, the format is roughly equivalent to the combination of a Variations2
Container concatenated with its associated Instantiations and Media
Objects. However, it separates information about the physical order of
the media from the logical structure, so it contains something like
the Work Structure and Bindings as well.