Grazing has two distinct meanings. First, grazing is a method of feeding in which a herbivore feeds on plants such as grasses, or other multicellular organisms such as algae. Many small selective herbivores follow larger grazers, who skim off the highest, tough growth of plants, exposing tender shoots. For terrestrial animals, grazing is normally distinguished from browsing in that grazing is eating grass or forbs, and browsing is eating woody twigs and leaves from trees and shrubs. Grazing differs from true predation because the organism being grazed upon is not generally killed. Grazing differs from parasitism as the two organisms do not live together, nor is the grazer necessarily so limited in what it can eat (see generalist and specialist species). Water animals that feed for example on algae found on stones are called grazers-scrapers. Grazers-scrapers feed also on microorganisms and dead organic matter on various substrates. Second, grazing is a method of agriculture in which domestic livestock are used to convert grass and other forage into meat, milk and other products.