Vegetarianism is the practice of abstaining from the consumption of meat (red meat, poultry, seafood, and the flesh of any other animal), and may also include abstention from by-products of animal slaughter.
Vegetarianism may be adopted for various reasons. Many people object to eating meat out of respect for sentient life. Such ethical motivations have been codified under various religious beliefs, as well as animal rights advocacy. Other motivations for vegetarianism are health-related, political, environmental, cultural, aesthetic, economic, or personal preference. There are variations of the diet as well: an ovo-lacto vegetarian diet includes both eggs and dairy products, an ovo-vegetarian diet includes eggs but not dairy products, and a lacto-vegetarian diet includes dairy products but not eggs. A strict vegetarian diet – referred to as vegan – excludes all animal products, including eggs and dairy. Avoidance of animal products may require dietary supplements to prevent deficiencies such as vitamin B12 deficiency, which leads to pernicious anemia. Psychologically, preference for vegetarian foods can be impacted by one's own socio-economic status and evolutionary factors.
Packaged and processed foods, such as cakes, cookies, candies, chocolate, yogurt, and marshmallows, often contain unfamiliar animal ingredients, and so may be a special concern for vegetarians due to the likelihood of such additives. Feelings among vegetarians may vary concerning these ingredients. Some vegetarians scrutinize product labels for animal-derived ingredients while others do not object to consuming cheese made with animal-derived rennet. Some vegetarians are unaware of animal-derived rennet being used in the production of cheese.
Semi-vegetarian diets consist largely of vegetarian foods but may include fish or poultry, or sometimes other meats, on an infrequent basis. Those with diets containing fish or poultry may define meat only as mammalian flesh and may identify with vegetarianism. A pescetarian diet has been described as "fish but no other meat". The common-use association between such diets and vegetarianism has led vegetarian groups such as the Vegetarian Society to state that diets containing these ingredients are not vegetarian, because fish and birds are also animals.
The first written use of the term "vegetarian" originated in the early 19th century, when authors referred to a vegetable regimen diet. Modern dictionaries explain its origin as a compound of vegetable (adjective) and the suffix -arian (in the sense of agrarian). The term was popularized with the foundation of the Vegetarian Society in Manchester in 1847, although it may have appeared in print before 1847. The earliest occurrences of the term seem to be related to Alcott House—a school on the north side of Ham Common, London—which was opened in July 1838 by James Pierrepont Greaves. From 1841, it was known as A Concordium, or Industry Harmony College, from which time the institution began to publish its own pamphlet entitled The Healthian, which provides some of the earliest appearances of the term "vegetarian".