A list item is a type of parameter that allows you to select an item from a specific list which was defined in another parameter.
For example:
- Parameter ´Rows´ --> Profit and Loss (as shown on the screenshot)
- Parameter ´Default Selected Item´ --> Profit
The parameter ´Default Selected Item´ is in this case of type List Item so you will be only allowed to select items from the Profit and Loss list.