The Summary is a global overview of the session, allowing for a good "bird's eye" view of where in time and tracks the work happens.
Each horizontal line represents a track in the session, with the colored bars being the audio and MIDI regions, colored as per their track's color setting.
Two yellow vertical lines show the position of the Start and End markers, defining the session's length. The red line shows the playhead's position.
The transparent white rectangle represents what's actually displayed in the Editor window, i.e. what part of the session is being looked at on screen.
The Summary also doubles as a navigator: