Resident pages which are private only to this process
Resident pages which may be shared with other processes.
Resident pages which are currently being shared with other processes. This is a subset of the Shareable Working Set.
Windows today uses several hints to help the operating system manage memory. One of these is reducing the working set when a process is not in use. For example, if you minimize a windows application, Windows will automatically release the working set of that application to the OS. If there is plenty of RAM, this has little effect; however, when memory is tight, the OS uses this information to decide which pages to page out first. (You can test this yourself - run Outlook, and check its memory usage. Then minimize it. Watch the working set shrink to a very small size).
--memory-model=high Never voluntarily relinquish memory
--memory-model=medium Voluntarily reduce working set when switching tabs
--memory-model=low Voluntarily reduce working set when switching tabs and also when the browser is not actively being used.