Here's why:

* Lives on or within another living organism: Parasites rely on their host for survival, living either on the surface (ectoparasites) or inside (endoparasites).

* At the expense of the organism: Parasites gain nourishment and shelter from their host, often harming the host in the process.

Examples include:

* Animals: Fleas, ticks, tapeworms, roundworms

* Plants: Mistletoe, dodder

Let me know if you'd like to learn more about parasites!