Frame sets
Definition:
1. Frames divide a Web browser window into sections that contain separate pages. Using frames, you can make your page layout more visually interesting and help viewers navigate in your Web site. Since the content of each frame is a separate page (and separate file) with its own URL, it can be changed and scrolled independently of the pages in other frames. For example, you can use frames to create an onscreen navigation aid or table of contents that remains visible in one frame while the viewer scrolls through the page in another frame.
Example

2. Inline frames enable you to insert a frame within a a non-frameset page.
Example