An enumeration is a hard-code fixed list in the app model. Which can be used in the model to constrain, filter or make decisions in your application front-end, logic and security. This list can be USED by users of the running app. It cannot be CHANGED by the users.
If you want to have an dynamic pick list in you app: create a new entity with a value attribute and create a reference between the data entity you have and this new entity and use the reference selector to select a value instead of a dropdown.