Prep: People who prepare food that will later be used for cooking food that actually goes out to the table.
Pantry: People who put together food and plates (typically salds, cold apps and desserts) that go out to the table.
So if you had, say, shrimp cocktails coming out of your pantry station. The prep person might be cleaning the shrimp, poaching them, and making the cocktail sauce. But the pantry person is actually on the line (or station, depending on the kitchen) and plating the things as they are sold.