References point to the same object, while copied data is a separate instance.
When you assign one object reference to another, both references point to the same object. Changes via one reference affect the other. For instance, if two `CartItem` objects reference the same `Product`, updating the product's price through one `CartItem` affects the other. In contrast, copying data creates an independent instance, so changes don't affect the original.
Additional Notes
What’s the difference between reference and copied data?