Heatmaps provide visual representation of user interactions with elements of a webpage. The color scale ranges from blue (not popular) to red (very popular).

Heatmaps allow you to quickly assess which elements website users click on, ignore, scroll thorough and more.

Here is the example of heat map based on the cursor movement:

Here is the information about heat map feature in Piwik PRO:
https://help.piwik.pro/support/integrations/smartlook-integration-session-recordings-heatmaps/