The MEP Metric 2.1 content is the Metric Fabircation content that ships with Revit 2018.

You can find it in the following folders of the install media...

32-bit media...

.\Revit\x86\MEP_Fab_M.msi

64-bit media...

.\Revit\x64\MEP_Fab_M.msi

If you installed Revit, the content should be located here unless you removed it....

C:\Users\Public\Documents\Autodesk\Fabrication 2018\Revit MEP Metric Content\V2.1

Or you can download it from Autodesk here....

https://knowledge.autodesk.com/support/revit-products/getting-started/caas/CloudHelp/cloudhelp/2018/...