Heatmaps track the movement of a thing over a geographical region. In this map, red tracks are areas in which a thing stayed for long periods, while in green areas the thing was barely seen.
Since the widget shows the travel of a thing, the parameter used to configure this widgets has to represent geographical coordinates. Luckily, Omnyvore filters out all the non-geographical parameters from the list, so you can safely choose a suitable parameter.
Remember to select exactly one parameter. Otherwise, you will not be able to save the widget.
Textual (usually short) description for what the heatmap shows. It will be visualised in the widget header.
For an exhaustive list of the widgets you can use in Omnyvore, please refer to the Available widgets subsection.