This is a text string reporting the free space on the boot volume needed to save a memory dump in the event of a crash, formatted as a number followed by MB or GB. An administrator uses it to confirm the boot drive actually has enough free disk space, separate from the paging file's own configured size, to successfully write a dump file when a crash occurs. For example, a boot volume nearly full of other data could still fail to save a crash dump even with a correctly sized paging file, if this reported free space requirement isn't met.