There is only one file type that uses the .MSD extension:
Map Service Definition File
Published map file created by ArcGIS Desktop, a software suite used to create maps and process geospatial data; contains a map that has been published from an .MXD map document; created for ArcGIS Server, which hosts the map for real-time viewing over a network.
| Software's name | License | Platforms |
|---|---|---|
ESRI ArcGIS for Desktop |
Commercial |  |
ESRI ArcGIS Server |
Paid | |
Updated: January 24, 2011