What type of relationship is defined by both species benefiting from their interaction?

The relationship described, where both species benefit from their interaction, is known as mutualism. In mutualistic relationships, the interaction enhances the fitness of both species involved. For example, the relationship between bees and flowering plants is a classic example of mutualism; bees receive nectar for food while simultaneously helping to pollinate the plants, facilitating their reproduction.

In contrast, parasitism is a relationship where one species benefits at the expense of the other, commensalism involves one species benefiting without significantly affecting the other, and neutralism refers to interactions where both species are unaffected. Thus, mutualism is the only relationship in which both parties gain advantages, making it the correct answer.