ZoneMinder has historically used IPC shared memory for shared data between processes. This has it's advantages and limitations. This version of ZoneMinder can use an alternate method, mapped memory, instead with can be enabled with the --enable--mmap directive to configure. This requires less system configuration and is generally more flexible. However it requires each shared data segment to map onto a filesystem file. This option indicates where those mapped files go. You should ensure that this location has sufficient space for these files and for the best performance it should be a tmpfs file system or ramdisk otherwise disk access may render this method slower than the regular shared memory one.