Dynamic Groups are used with Database pens. They allow you to apply a dynamic condition, like using a WHERE clause, to a subset of pens. For each pen group, a dynamic string property will appear in the Property Editor under Custom Properties of your Easy Chart component. You can create a WHERE clause that will search the database and return values if the pens meet a true condition.
Property Editor - Custom Properties - Where Clause for Dynamic Group Property
To learn more about Dynamic Groups, refer to the Easy Chart section.