The file extension .mdmp indicates an MDMP file. The MDMP file type, commonly referred to as a "minidump" file, is a compressed file type created by Windows XP and above following a program error or crash.
The MDMP file contains information that is dumped by the affected program's memory space and saves any information about the error, which can be used for debugging. MDMP files can also be sent to Microsoft as part of a debugging process.
MDMP files can be analyzed using WinDmp, a debugging program that is a component of the Microsoft Windows software development. These files are normally saved with an uncompressed HDMP version of the same file.