The term "poisonous plants" refers to plants that contain substances which can cause harm or injury if ingested, touched, or inhaled. These plants produce chemicals such as alkaloids, glycosides, and terpenes, which can have a range of effects on humans and animals, from mild irritation to severe illness or even death. Some common examples of poisonous plants include foxglove (which contains digitalis), oleander (a highly toxic plant containing cardiac glycosides), and rhododendron (which can cause vomiting and diarrhea if ingested). It is essential to be aware of these plants, especially in areas where children or pets may be present, as accidental exposure can occur.