We are presenting the documentation for MMODS-O, an ontology derived from the Metadata Object Description Schema (MODS, version 3.8), which is an XML Schema by The Library of Congress. The XML Schema concerns metadata pertaining to bibliographic elements, however it is also used for other purposes, for instance LCACommons which is an interagency community that focues on Life Cycle Analysis, National Agricultural Library -- require the metadata to be in MODS format.  Our motivation for developing this ontology -- including how it relates to previous attempts -- will be described elsewhere. This documentation is intended for readers who are familiar with MODS XML schema.