This could mean 'address space reserved but not committed'. Committed address space is often much smaller than reserved address space - think of how the stack s

This could mean 'address space reserved but not committed'. Committed address space is often much smaller than reserved address space - think of how the stack starts out with very little actual memory in use, and then grows as unused pages are first touched. That mechanism ensures that spinning up a temporary thread with a shallow stack doesn't eat up 8mb of physical memory instantly. The pages are also zeroed on-demand when committed, which ensures thread creation doesn't first require 8mb of pages to be zeroed (There are workarounds for that as well).