NOTE: As a matter of fact, this post is copied from an answer in Stack Overflow, click here. I think this answer is a good example of how to answer question in Stack Overflow, it is distinct, sort of elegant, and most important, it gives you the right answer.
<a> element is invalid HTML unless it has either an href or name attribute.
If you want it to render correctly as a link (ie underlined, hand pointer, etc), then it will only do so if it has a href attribute.
Code like this is therefore sometimes used as a way of making a link, but without having to provide an actual URL in the href attribute. The developer obviously wanted the link itself not to do anything, and this was the easiest way he knew.
<a> tag link.
Some developers use href='#' for the same purpose, but this causes the browser to jump to the top of the page, which may not be wanted. And he couldn't simply leave the href blank, because href='' is a link back to the current page (ie it causes a page refresh).