The widely accepted and used definition in economics refers to products that are identical or nearly identical, or more specifically, whose functions and costs of production are nearly identical. Student editions of software, for instance, are often functionally limited, but it is widely listed as an example of price discrimination. Some econ textbooks will make a distinction of "pure price discrimination," which requires the products to be literally identical. Note that the identity function for products is not always obvious.

I maintain that the iPhone's storage pricing is a clear example of price discrimination.