ToolTip is a little non-modal pop-up that could be used to display additional information, that is usually hidden.
Major toolTip features:

- Tool-tip content may be pre-rendered on a page (client mode) or loaded on separate Ajax request (ajax mode)
- In "ajax" mode default content could be shown while request is executed
- Parameters can be passed to the server during an ajax request
- Tooltip look is fully customizable using both - Richfaces skins and CSS style classes

ToolTip example