About iFrames

Frames are HTML elements that allow a visual HTML Browser window to be split into segments, each of which can show a different document. This allows for lower bandwidth use, as repeating parts of a layout can be used in one frame, while variable content is displayed in another.

An iFrame, or inline frame places another HTML document into a frame. Unlike an object element, an inline frame can be the "target" frame for links defined by other elements and it can be selected by the user agent as the focus for printing, viewing its source etc. The text you are viewing right now is located inside an inline frame, its location being 'about.php'.

Source: Wikipedia