A weed is a plant considered unwanted in human-controlled settings, such as farm fields, gardens, lawns, and parks. The derogatory term ‘weed’ is also applied to any plant that grows or reproduces aggressively or is invasive outside its native habitat. Invasive species are largely a consequence of human activity: plants and seeds brought by people on purpose or by accident to an area, where they might not have natural competitors and thus will grow unstoppably.