The Browser Object Model (BOM) is a browser-specific convention referring to all the objects exposed by the web browser.
[1] Unlike the Document Object Model, there is no standard for implementation and no strict definition, so browser vendors are free to implement the BOM in any way they wish.
[2] That which we see as a window displaying a document, the browser program sees as a hierarchical collection of objects.
It is part of a larger collection of objects that the browser makes use of.
Some of its fields are objects themselves that describe the document and related information.