From Htmlpedia

This tag adds an underline effect to the text within.

For example:

<u> This is some underlined text </u>

Would show up like so:

This is some underlined text

Note the fact that the underlined text looks similar to a hyperlink. This is especially true if the text is the standard blue color.

The command that will produce this same effect in CSS is text-decoration.

For example:

<u style="text-decoration:none;"> This is some text in an underline tag </u>

would show up like so:

This is some text in an underline tag

The "text-decoration:none;" completely negagates the styling of the <u> tag.