_An inline frame places another HTML document in 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 content of the element is used as alternative text to be displayed if the browser does not support iframes.
First introduced by Microsoft Internet Explorer in 1997, standardized in HTML 4.0 Transitional, allowed in HTML 5._
Youtube uses iframes to post videos on a site. If you check their embed code, you will see that it is inside an iframe. Paulie_D put it the best. Youtube would be the best example. The video is stored on the youtube website. It’s in their servers. You you can watch the video on any website anywhere. Thanks to an Iframe. It holds the content and get the information it needs from youtube and sends that information to your site.