There are over 12,400,000 website pages that don’t have a title, using the default “Untitled Document” because the page isn’t using the <title> HTML tag. The authors of websites should read The Importance of the Hypertext Document Title:
The title is the element that identifies globally the document’s content. It is one of the most important contributors to a positive user experience for a Website’s visitors. Ironically, the title is commonly overlooked, or not considered, possibly because browsers don’t use the title within the document’s body.