In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna. Examples of such interactions include a cell being host to a virus, a bean plant hosting helpful nitrogen-fixing bacteria, and animals as hosts to parasitic worms, e.g. nematodes. The word “guest” is also (more rarely) used in biology to refer to the organism that lives with the host.