Symbiosis means living together. Symbiotic relationships are close or intimate relationships between members of two different species.
These relationships have co-evolved. This means that the relationship and dependency has developed over many years. Symbiotic relationships usually benefit at least one of the individuals involved.
There are two categories of symbiosis:
Parasitism – one species, the parasite, benefits at the expense of the other species, the host.
Mutualism – both species benefit from the relationship.