Ecoterrorism (also known as "monkeywrenching"' to many of its practitioners) is the act of destruction of infrastructure and equipment involved in industrial or scientific activities perceived to be unnecessarily damaging to the environment. Most people identified as ecoterrorists tend to be leftist, often closely associated with the animal rights and hard green movements, and they generally target objects and sites rather than people, with the objective of causing economic rather than human damage.
The term is usually associated with (and correctly used to refer to) two groups, the Animal Liberation Front and the Earth Liberation Front. It is also sometimes erroneously linked to the Unabomber, though his primitivism was chiefly rooted in human psychology, with only passing reference to ecological concerns. However, anti-environmentalists also use the label as a snarl word for a variety of other groups they don't like, such as PETA, Greenpeace, the Sea Shepherd Conservation Society, Earth First!, and the Rainforest Action Network, among others. It is unclear to what extent there is an actual epidemic of ecoterrorism, as opposed to much of it being a media-driven moral panic.
The term itself is a neologism invented by anti-environmentalist activists who felt the term "monkeywrenching" was too soft or had good connotations. Furthermore, "monkeywrenching" was associated with nonviolent vandalism such as pulling up survey stakes, and with direct action protests such as tree sitting, and a harder term was needed for things like arson and bombings. However, it should be noted that the term's adoption by anti-environmentalists was intended to blur the distinction between the two, not clarify it.