A '''weed''' is a [[plant]] considered undesirable. Weeds are commonly unwanted plants in human-controlled settings, such as [[agriculture|farm fields]], [[garden]]s, [[lawn]]s, and [[park]]s. Weeds have no botanical classification value, since a plant that is a weed in one context is ''not'' a weed when growing where it is wanted. A number of plants that many consider weeds are often intentionally grown in gardens and other cultivated settings. It is applied to any plant that grows or reproduces aggressively, or is [[Invasive species|outside its native habitat]].<ref>{{cite book | isbn = 0-7167-1031-5 | last = Janick | first = Jules | title = Horticultural Science | location = San Francisco | publisher = W.H. Freeman | year = 1979 | page = 308 | edition = 3rd}}</ref> The term is occasionally used to broadly describe species outside the plant kingdom that can live in diverse environments and reproduce quickly, and has even been applied to [[humans]].<ref name=Quammen>{{citation |title=Planet of Weeds |author=David Quammen |work=Harper's Magazine |date=October 1998 |url=http://sep.csumb.edu/class/ESSP645/readings/Quammen%201998.pdf |accessdate=November 15, 2012}}</ref>