Description Box using "onmouseover"

Assuming popup is the ID of your "description box":

HTML

<div id="parent"> <!-- This is the main container, to mouse over -->
<div id="popup" style="display: none">description text here</div>
</div>

JavaScript

var e = document.getElementById('parent');
e.onmouseover = function() {
  document.getElementById('popup').style.display = 'block';
}
e.onmouseout = function() {
  document.getElementById('popup').style.display = 'none';
}

Alternatively you can get rid of JavaScript entirely and do it just with CSS:

CSS

#parent #popup {
  display: none;
}

#parent:hover #popup {
  display: block;
}

Well, I made a simple two liner script for this, Its small and does what u want.

Check it http://jsfiddle.net/9RxLM/

Its a jquery solution :D

Although not necessarily a JavaScript solution, there is also a "title" global tag attribute that may be helpful.

<a href="https://stackoverflow.com/questions/3559467/description-box-on-mouseover" title="This is a title.">Mouseover me</a>

Mouseover me