Parasitism, where the parasite benefits and the host is hurt.
Commensalism, one species benefits and the other is not helped or hurt.
Mutualism, both species benefit.
An example of Commensalism is the Pearlfish and Sea Cucumber. The Pearlfish spends all day in the alimentary tract (intestines) of the sea cucumber and at night emerges from its anus to feed on crustaceans.