The document discusses HTML frames, which divide the browser window into multiple sections that can each load a separate HTML document. Frames are defined using the <frameset> tag instead of <body>, with the rows or cols attribute specifying how to divide the window horizontally or vertically into frames. Each frame is indicated by a <frame> tag specifying the HTML document to load. Examples are given showing how to create documents with three frames arranged horizontally using rows, and vertically using cols.