Here's a breakdown of what that means:

* Parasite: An organism that lives in or on another organism (the host) and benefits by deriving nutrients at the host's expense.

* Host: The organism that the parasite lives on or in.

Examples of parasites include:

* Viruses: These are non-living entities that require a host cell to replicate.

* Bacteria: Some bacteria are parasitic, causing diseases like tuberculosis or Lyme disease.

* Protozoa: Single-celled eukaryotic organisms, such as the parasite that causes malaria.

* Helminths: These are parasitic worms, such as tapeworms or roundworms.

It's important to note that not all organisms that live in or on other organisms are parasites. Some have a mutualistic relationship, where both organisms benefit, or a commensal relationship, where one organism benefits while the other is neither harmed nor helped.