Epiphytes are plants that grow on other plants, such as trees, primarily for physical support.
The key characteristic of the epiphyte-host relationship is that the epiphyte benefits (e.g., by gaining access to sunlight), while the host plant is generally neither harmed nor helped.
This type of relationship, where one organism benefits and the other is unaffected, is defined as Commensalism. This is the most common type of biotic interaction exhibited by epiphytes.
Therefore, most epiphytes are prime examples of Commensalism.