The relationship where one organism is harmed is called parasitism.

Here's a breakdown:

* Parasitism: One organism (the parasite) benefits by living in or on another organism (the host), causing harm to the host.

Examples of Parasitism:

* Ticks on a dog: The tick feeds on the dog's blood, harming the dog by potentially transmitting diseases.

* Tapeworms in a human: The tapeworm lives in the human's intestines, absorbing nutrients from the host and causing health problems.

* Mistletoe on a tree: The mistletoe draws water and nutrients from the tree, potentially weakening it.

Let me know if you'd like to know more about different types of relationships between organisms!