Browser Object Model
There is a hierarchy of browser objects that are used to manipulate methods and properties associated with the Web browser itself. The top level object in the BOM is the window object. The window object represents the browser window. All other browser objects are contained within the window object. The window object includes a number of properties and methods that can be used to control the Web browser. A good portion of client-side Web develop is in working with the properties and methods associated with the browser itself, with its windows, and with the documents that occupy them.
The example shown in the above two statements means the same.