Just recently for one of my websites I did a bit of research to see how easy it’ll be to add keyword tooltips. What I was looking for was, when a user hovers over a keyword within a piece of content a nicely styled tooltip appears.
There are a few modules on drupal.org that integrate with jQuery popup and tooltip plugins, however, I ended up choosing the Tipsy module. As the name suggests, the Tipsy module uses a jQuery plugin called Tipsy and the jQuery plugin creates Facebook-style tooltips.
drush dl tipsy
<a class="popup" title="Message will appear in the tooltip">Link text</a>