Commensalism is an interaction between two different species of living organisms in which one benefits nor is harmed by it.

One organism benefits and is called the commensal.The other organism is not affected and is called the host.

For example:Commensalism exists between remora fish and sharks.

The remora fish attaches itself to a shark and bebefits from feeding on food scattered by the shark.

The shark neither bebefits from the remora fish nor is harmed by it.

Commensalism may involve two animals or two plants:Remora fish and shark

Orchid and tree