A heatmap is, in digital marketing context, a visualization map allowing to see where and how visitors interact with a webpage. The brighter or hotter an area is, the more interactions there are. Red areas are the areas with the most interactions and a cold color like blue marks areas with less activity. Heatmaps may be also used for emails.
Interactions taken into account can be mouse clicks, mouse movements or gazes through points of fixation.
There are mainly two kinds of heatmaps used in usability or consumer experience studies according to the type of interactions measured and tracked.
The most known is the eye tracking heatmap. For a sample of users it shows where gaze fixations occurs. For more details and examples see eye tracking heatmap.
An example of eye tracking heatmap with points of fixation:
Source image Frontend
An example of video heatmap for Google SERPs :
A heatmap for mobile :
The other form of heatmap is the click heatmap. It shows for a sample of visitors where clicks occur.
An example of clicks heatmap:
Source image Crazy Egg
Eye tracking or gaze heatmaps are produced by the way of laboratory experiments with a limited sample of users- often between 10 and 20. Click heatmaps are built server side by tag implementations. They are simpler to create and can be based upon hundreds or thousands of visits.
For more details on processes and usages, see eye tracking and mouse tracking.
Heatmaps were used before Internet advent for marketing purposes with eye tracking studies (packaging, ads, etc.).
An example of mouse move tracking:
Source image Clicktale