An association between two individuals or populations where both benefit and neither can survive without the other is:
mutualism
Mutualism is the association that is mutually beneficial for both the organisms and the relationship is crucial for the existence of their species. For eg. bees and flowers, without the bees plants do not have pollinators for the propagation of their species and without flowers, the bees do not have sustenance. Competition, unlike mutualism, is a relationship that is harmful to both the species involved. Commensalism, on the other hand, is a relationship that is beneficial to one organism while the other is unaffected; for eg. the sea anemone and the clown fish. Ammensalism, unlike commensalism, harms one of the partners in the relationship while the other is unaffected, for eg. antibiotics produced by some fungi that kill the bacteria.