In John Wyndham's “The Day of the Triffids,” the mobile plants are called triffids.
Triffids are fictional, tall, venomous, carnivorous plants that can move and attack people with a poisonous stinger. They are central to Wyndham's 1951 post-apocalyptic novel, in which most of the world's population is blinded after watching a mysterious celestial display.
The protagonist, Bill Masen, is a biologist who has worked with triffids and understands their behavior. Their danger is intensified by the collapse of human society, but the plants are not simply wild monsters: people cultivate them because they produce valuable oil. This economic usefulness helps explain why triffids were distributed widely before the catastrophe.
The name refers to the plants' three-legged appearance. In the novel, their precise origins are mysterious, although Bill suspects Soviet biological engineering. Adaptations changed that backstory: the 1962 film presents the triffids as extraterrestrial, while later television versions offer different explanations. “Triffid” is also used in British English for a large, invasive, or menacing-looking plant.