"Mode" refers to "docking mode". A Mode is a place in a window (in MDI mode, a place between splitters - in SDI mode, a frame) which is usually represented by a tabbed container. It is represented by the class org.openide.windows.Mode

A Mode is not a GUI component. There is no legitimate programmatic way to fetch the component that represents a Mode on-screen, and the windowing system makes no guarantees about what that component is.

The name "Mode" is a bit unfortunate. When you hear "Mode," think tabbed container and you'll be fine.

Modes can contain one or more TopComponents. They may be visible or non-visible at any given time.

Source: NetBeans FAQ