u

The u HTML element represents a span of text with an unarticulated, though explicitly rendered, non-textual annotation, such as labeling the text as being a proper name in Chinese text (a Chinese proper name mark), or labeling the text as being misspelt.

<u attribute-name="attribute-value"></u>

Global

u {
    text-decoration: underline;
}

Web Hypertext Application Technology Working Group (WHATWG)