What is an iFrame used for in HTML?

An iFrame, or inline frame, is utilized in HTML primarily for embedding one HTML document within another HTML document. The strength of using an iFrame lies in its ability to display content from a different source, which could include another web page or app, without having to navigate away from the current page. This allows for a seamless integration of external content, such as videos, maps, or advertisements, directly within the existing layout of a website.

For instance, if a website wants to incorporate a YouTube video, it can simply embed the iFrame that points to the video link. This keeps users engaged on the original site while still providing rich, interactive content. The iFrame acts as a window to the external content, maintaining the context of the original page and allowing users to interact with both the parent document and the embedded content simultaneously.

The other choices do not accurately represent the function of an iFrame. Displaying images pertains to the use of the <img> tag. Creating navigation links involves using <a> tags to define hyperlinks. Building forms requires elements like <form>, <input>, and <textarea>. Therefore, the unique role of the iFrame in embedding content makes it the correct answer.