Here's a breakdown:

* 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 provides sustenance and shelter to a parasite.

For example:

* A tick is a parasite that feeds on the blood of a deer, which is the host.

* A tapeworm is a parasite that lives in the intestines of a human, which is the host.

Hosts can be:

* Definitive hosts: These hosts harbor the adult stage of the parasite.

* Intermediate hosts: These hosts harbor larval stages of the parasite.

It's important to note that parasitism is a complex relationship. The parasite can cause harm to the host, but the host often survives, and the relationship can continue for a long time.