A heat map is a data visualization technique that shows magnitude of a phenomenon as color in two dimensions. The variation in color may be by hue or intensity, giving obvious visual cues to the reader about how the phenomenon is clustered or varies over space.
You can find a more in depth explanation about the Heat map on this page:
Properties of Heat Map
Property Name
Data type
Type
Description
Data Source
List
Data model
List containing all labels, values and series.
Value
Number
Expression
Set the value of the heat map.
Label
Text
Expression
The label on the x axis.
Series
Text
Expression
This field is used to create different groups from the same data source. The series are part of the y axis.
Color
Text
Expression
Color of the item. Note that each series can only have a single color. The first color of an item part of the series will be used.
Height
Number
Expression
Can be set to number, percentage of container or pixels.