According to Merriam-Webster Online Dictionary, defined as the relationship between two different kinds of living things that live together and depend on each other.
There are three types of symbiotic relationships
Mutualism - both species involved in the interaction benefit
Commensalism - where one of the species involved benefits, while the other receives no harm or gain from the relationship
Parasitism - where one of the species acts as a host and is harmed (often killed) due to the interaction