Which of the following tags is used to define an emphasized text?

The tag used to define emphasized text is the <em> tag. This tag is semantically used in HTML to indicate that the enclosed text should be emphasized, which typically affects how it is rendered in a browser—often displayed in italics. The use of <em> reflects a stronger meaning or importance regarding the content within it, allowing not just visual emphasis but also conveying significance to assistive technologies like screen readers.

In contrast, the <strong> tag is used for indicating strong importance, often rendered in bold, but its purpose is distinct from that of <em>. The <b> tag is a purely stylistic tag that renders text in bold without implying any additional emphasis or importance. Lastly, <highlight> is not a recognized HTML tag, and therefore cannot be used to define emphasized text.