What does the <mark> tag signify in HTML?

The tag in HTML is utilized to highlight or mark text for reference or emphasis, which is why the correct answer identifies it as designating highlighted text. This tag is particularly useful for drawing attention to specific parts of a document, such as keywords or important information. When text is wrapped in a tag, it is typically displayed with a yellow background in many web browsers, visually indicating that it has been emphasized or is of significance to the reader.

The purpose behind using the tag aligns with enhancing user experience and accessibility, making it easier for users to identify important content in a text-heavy document. This function contrasts with functionality provided by other tags in HTML, such as those used for underlining, bolding, or linking text, which serve different design and structural roles in web development.