HTML <iframe> src Attribute

<iframe src="demo.html">
  Your browser does not support iframe element.
</iframe>

Meaning

The src attribute contains the URL of the content to be displayed in the floating frame. If absent, the frame is blank.

<iframe src="URL">

Value	Description
URL	Specifies the URL of the document in the <iframe>. An absolute URL - navigate to within or another web site ( href="http://www.example.com/index.html") A relative URL - navigate to within a web site ( href="index.html")