A Windows minidump is a small file that is generated every time the Windows operating system unexpectedly encounters an error, such as during "blue screen of death" (BSoD) crashes. The file contains information regarding the nature of the error, such as the state of the system right before and possibly during the crash. This contains information like running services and processes as well as the resources being used by each.
Techopedia explains Windows Minidump
A Windows minidump is a file created to help a user diagnose the circumstances behind a crash, specifically in the Windows operating system. It contains rich information about the system right before and during the crash to help pinpoint the problem. Information like applications and programs running, resource consumption and processor state can be seen in the minidump file. A minidump may not contain as much information as a full crash dump file, but usually suffices to help quickly diagnose a problem. Other applications are also able to create minidumps that contain varying types of information.
To read a minidump file, the binaries and symbol files must be available for the debugger software. Windows, particularly 2000 and XP, has a built-in minidump debugger called dumpchk. The Windows minidump file is found in the "minidump" subfolder of the Windows system folder (e.g., "C:\Windows\minidump") and looks somewhat similar to this: Mini030915-01.dmp. The first two digits ("03") stand for the month, the second ("09") for the day and the third ("15") for the year. The "-01" stands for the number of minidump file in case more than one file has been created on the same day.