Dynamic data fields are drop lists on a form that are automatically populated with values that come from either:
Dynamic data fields are suitable for scenarios where your drop lists needs to be dynamically loaded with values that come from somewhere else. Say for example you have a company that sells educational courses, and you need your forms to always display the most up to date course listings, where those listings come from your own system or I.T department).
Dependencies between dynamic data fields
If the source of data is an external API you can also define parent dependency relationships between multiple drop lists so that if one drop list changes, another call will automatically be made to your API to pull the data needed for the "dependent" child drop list to show the correct list of results.
External API Example
Here's an example of of when dynamic data fields are useful. In the example scenario below we have two drop lists - "University Campus", and "Course of Interest". We want to automatically list only "University Campuses" that we have an active relationship with according to some criteria, and for the "Course of Interest" drop list we want this to automatically list all active courses that exist under the University that has been selected.
As long as we have access to a web service that exposes this "active" list of universities, and "course of interest" information in the correct format, we can incorporate that data into our forms.
Note: If instead you just require basic showing/hiding of drop lists depending on certain scenarios you may want to instead check out the option of using "Conditional Logic" to simply show hide relevant fields that you have previously populated with static values.
How to setup
In the following article please checkout How to setup dynamic data fields