What term describes unwanted organisms that can cause harm to humans, animals, or structures?

The term that best describes unwanted organisms that can cause harm to humans, animals, or structures is "pest." Pests are typically defined as any organisms that negatively impact human activities, wellbeing, or the environment, making them an important focus in pest control practices. This can include insects, rodents, weeds, and even fungi, all of which can pose various risks such as disease transmission, property damage, or agricultural loss.

Infestation refers specifically to the presence of a large number of pests in an area, indicating that the pests have established themselves and are multiplying, but it does not describe the organisms themselves. Weed specifically defines unwanted plants that compete with cultivated plants, so it doesn't broadly cover the range of organisms harmful to humans or structures. Nuisance typically describes something that causes inconvenience or annoyance but doesn't necessarily involve the potential for harm, limiting its relevance regarding organisms that can inflict damage or health risks. Thus, using "pest" captures the broader implications of harmful organisms effectively.