The correct answer is B: commensal.

Explanation:
In this association, organism X benefits from the waste products of organism Y, while organism Y is neither harmed nor benefited. This describes commensalism, which is a type of symbiotic relationship where one organism benefits, and the other is neither helped nor harmed.

Here’s why the other options are not correct:
- A. Symbiont: A symbiont refers to an organism involved in a symbiotic relationship, which could be mutualistic, commensal, or parasitic. In this case, commensalism is the specific relationship being described.
- C. Saprophyte: A saprophyte feeds on dead or decaying organic matter, but here X is feeding on waste products, not necessarily dead matter.
- D. Parasite: A parasite benefits at the expense of the host, which is not the case here, as organism Y is not harmed.
- E. Epiphyte: An epiphyte is an organism that grows on another plant (typically a type of plant like moss), but it does not feed on the other organism’s waste products.

Thus, the correct term for organism X is commensal.