This question is about terminology.
Assume the following scenario. A research participant is asked to choose one out of four options: products A and B in packagings X and Y. That is, the choice (denote it as O) is the combination A&X, A&Y, B&X, B&Y.
The researcher wants to find out if the choice of the product is independent of the choice of the packaging. That is, $H_0: P(A| X) = P(A | Y)$
Is it a "between-subject" or a "within-subject" design?