A crosswalk is "In the management of metadata, a human-generated chart or diagram indicating equivalencies and relationships between the data elements of two or more metadata standards, for example, between FGDC content standards for digital geospatial metadata and USMARC. Crosswalks enable search engines to operate across databases that use dissimilar record formats."
Reitz, J.M. (2013, January 10). ODLIS: Online Dictionary for Library and Information Science. Retrieved from http://www.abc-clio.com/ODLIS/odlis_c.aspx
The Getty's Metadata Standards Crosswalk - includes a wide variety of metadata standards
MODS Conversions - mappings and XSLT stylesheets to and from MODS to other standards, including Dublin Core and MARC