What is a naturally occurring poison produced by organisms called?

The term that refers to a naturally occurring poison produced by organisms is "toxin." Toxins are biological in origin and can be produced by various organisms, including bacteria, plants, and animals, to defend themselves or to incapacitate or kill prey. For example, the poison found in certain plants or the neurotoxins produced by some species of pufferfish fall under this definition.

The other terms relate to concepts that are related but do not specifically describe a naturally occurring poison. "Toxicity" refers to the degree to which a substance can harm organisms, so it describes the potential for harm rather than the substance itself. "Toxicant" typically refers to man-made or synthetic substances that produce toxic effects but does not specifically indicate a natural origin. "Venom" refers to a specific type of toxin that is actively injected through a bite or sting, which distinguishes it from other types of toxins that may not be delivered in the same manner.

Thus, the correct answer, "toxin," specifically encompasses the definition of a naturally occurring poison produced by an organism.