A list definition is a multi-purpose object that lets you create a list of items to use in a manual property definition. After you create a list definition, values can be selected from the list without having to enter them manually each time.
For example, if you create a predefined list of acceptable values for paint color or manufacturers, you remove the risk of forgetting a correct name or making a typographical error when setting up manual properties. Create the list once, copy it into the appropriate project files as needed, and then you can easily select values for manual properties when you add them to property definitions.