Tooltip is represented with the 
icon.
A tooltip is displayed when you hover over a Mark.
Any field that you drop on Tooltip is added to the tooltip box. The fields in the tooltip are always aggregated. However, you can still add a Dimension to the tooltip. Tableau uses a special aggregation, ATTR, to display it. This aggregation returns the value if it's unique, or shows * if not. That symbol means that there is more than one value.
Clicking on the Tooltip button opens a window where you can edit the text and change a few options. Those options allow you to:
- Choose whether you want to show the Tooltip
- Include the command buttons ...
