Explaining MALLOC_NANO

Could someone explain what 'MALLOC_NANO' is?

A snippet from the crash report this was contained in is here:

Crashed Thread:        50  myThread
 0x1722ac000 -        0x17244ffff
Exception Type:        EXC_BAD_ACCESS (SIGBUS)
Exception Codes:       KERN_PROTECTION_FAILURE at 0x0000600015c9e340
Exception Note:        EXC_CORPSE_NOTIFY

Termination Signal:    Bus error: 10
Termination Reason:    Namespace SIGNAL, Code 0xa
Terminating Process:   exc handler [35195]

VM Regions Near 0x600015c9e340:
    MALLOC_NANO              600008000000-600010000000 [128.0M] rw-/rwx SM=PRV  
--> MALLOC_NANO              600010000000-600018000000 [128.0M] rw-/rwx SM=SHM  
    MALLOC_NANO              600018000000-600020000000 [128.0M] rw-/rwx SM=PRV  

I'm guessing the root cause for this crash is using a deallocated object but I'd really like to just know more about MALLOC_NANO as I couldn't find much information elsewhere.

Much appreciated!