This Pseudo-class applies to elements or contexts that have no
content. An element is considered to have content if it is a container
element, and has at least one or more text or other elements inside
it. This is probably of limited usefulness for container elements
like DIV or BLOCKQUOTE, but for empty elements such as IMG it could
have more applications.
Another possible application:
Consider if a document is being constructed from database data - some
fields may or may not contain data, and in a case where there is no data
you wish to render this fact in a specific way.
Example
Ext/Doc: td:empty
{ border medium solid red;
background-color black }
In-Line: NA
Browser Peculiarities
Netscape 6.x: This pseudo-class does not apply to container elements
that have no content, like TD or TH, where it would seem to have its
most interesting use. (Bugzilla 26179)