Packaged and processed foods, such as cakes, cookies, candies, chocolate, yogurt, and marshmallows, often contain unfamiliar animal ingredients, so may be a special concern for vegetarians due to the likelihood of such additions. Often, prior to purchase or consumption, vegetarians will scrutinize products for animal-derived ingredients. Vegetarians' feelings vary with regard to these ingredients. For example, while some vegetarians may be unaware of animal-derived rennet's role in the production of cheese, and may therefore unknowingly consume the product, other vegetarians may not take issue with its consumption.
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 term "vegetarian" has been in use since sometime before the so far first discovered written use in 1839 to refer to what was previously described as a vegetable regimen or diet, for example in print in 1811. Modern dictionaries based on scientific linguistic principles have always explained its origin as an irregular compound of vegetable (in the adjectival sense of any plant still common today) and the suffix -arian (in the sense of "supporter, believer" as in humanitarian), but there were amateur attempts, even by a Latin scholar not trained in linguistics, to find other origins of the word.
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".