What term describes a behavior where one species benefits at a cost to another?

The correct term for a behavior where one species benefits at a cost to another is predation. In predation, one organism (the predator) kills and consumes another organism (the prey), resulting in a clear benefit for the predator while negatively impacting the prey.

Commensalism refers to a relationship where one species benefits while the other is neither helped nor harmed, so it does not fit the description of a cost to another species. Altruism describes behavior in which an individual sacrifices its own benefit for the good of another, which does not align with one species gaining at the expense of another. Competition is characterized by two or more species vying for the same resources, leading to a negative impact on one or both, but again, it does not specifically describe a relationship where one benefits at a cost directly to another in the same definitive way as predation does.