[javascript] What does href expression <a href="javascript:;"></a> do?

Refer to this:

<a href="Http://WWW.stackoverflow.com">Link to the website opened in different tab</a>
<a href="#MyDive">Link to the div in the page(look at the chaneged url)</a>
<a href="javascript:;">Nothing happens if there is no javaScript to render</a>