Symbiosis describes a close and long-term interaction between two different biological organisms. There are several types of symbiosis, including:

* Mutualism: Both organisms benefit from the relationship.

* Commensalism: One organism benefits, while the other is neither harmed nor helped.

* Parasitism: One organism benefits at the expense of the other.

The example you're thinking of is likely mutualism, where both organisms gain something from the partnership that helps them survive.