An orchid growing as an epiphyte on a mango branch and barnacles growing on the back of a whale are examples of:
Commensalism
The orchid growing as an epiphyte on a mango branch obtains its nutrients from the mango tree, however, it does not harm the mango tree, therefore their relationship benefits one partner, while the other is unaffected.
Similarly, the barnacle on the whale benefits from this relationship by obtaining home and free travel with access to food by growing on the whale and the whale itself is unaffected by this relationship.
These relationships are called commensalism. Ammensalism is when one organism is harmed while the other is unaffected. In competition both the organisms are harmed because competition causes a struggle for resources. And mutualism is a mutually beneficial relationship between organisms.