I think it has to do with the memory area concerned with pagefiles and Virtual memory: (control panal/sytems/proformance). space on your hd that Windows NT uses as if it were actual memory.
Swap files or pagefiles that go between the hd and ram when needed. It also configures the registry size and the memory you set can,if exceeded, halt! with a stop error, the Registry. the Pool, in the abstract, represents this process of where and how this allocated space functions as pagefile go in and out from ram to the virtual memory on the hd. this is just a general idea of the thing and all os's have mem pool variations on the same thing.