I find that entry in the memory allocation list of my computer (Workstation -> Device Manager -> View -> Resource by Type). It takes up 256MB of RAM and I'm wondering what's it good for.
From this Intel document
Root Port: A PCI Express Port, on a Root Complex, that maps a portion of the PCI Express interconnect Hierarchy through an associated virtual PCI-PCI Bridge.
Root Complex: An entity that includes a Host Bridge and one or more Root Ports.
Yeah, some circular definitions going on here.