Final answer:
If p(x) ⊆ p(y), then the relation between x and y is that x is a subset of y.
Step-by-step explanation:
If p(x) ⊆ p(y), then it means that every subset of set x is also a subset of set y. This implies that set x is a subset of set y, denoted as x ⊆ y. In other words, every element in x is also in y, but y may have additional elements that are not in x. Therefore, the relation between x and y is that x is a subset of y.