From http://www.w3schools.com (Copyright Refsnes Data)

HTML <u> tag

The u element is deprecated.

Example

Underline text with the <u> tag:

<p>Do not <u>underline</u> text if it is not a hyperlink!</p>

Try it yourself!

Definition and Usage

The <u> tag defines underlined text.

Browser Support

Internet Explorer Firefox Opera Google Chrome Safari

The <u> tag is supported in all major browsers.

Differences Between HTML and XHTML

The u element was deprecated in HTML 4.01, and is not supported in XHTML 1.0 Strict DTD.

Tips and Notes

Tip: Do not underline text! A user confuses it with a hyperlink!!

Standard Attributes

id, class, title, style, dir, lang, xml:lang

For a full description, go to Standard Attributes.

Event Attributes

onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove, onmouseout, onkeypress, onkeydown, onkeyup

For a full description, go to Event Attributes.

From http://www.w3schools.com (Copyright Refsnes Data)