Map Windows are the individual windows that actually contain the information that one views and edits. Map Windows are always contained within a Session. Just as Sessions inherit defaults from the project, Map Windows inherit defaults from the Session they are in. 

A Session can have one or more Map Windows associated with it.  The following image shows the "Forecast Precipitation" Map Window which belongs to the "Russian River" Session.

Map Window management is very similar to Session Management. The major difference is that Sessions use a minimal amount of memory to hold settings and lists of TINs to aggregate, while Map Windows can consume large amounts of memory when open. Large TIN models use significant resources as do the mapping layers that each Map Window maintains to make the program more responsive. If the computer used has limited memory or the Java virtual machine is configured to use a relatively small amount of memory, closing any unnecessary Map Windows is the most effective way to keep memory usage to a minimum.