Vegetarianism is the practice of abstaining from the consumption of meat (red meat, poultry, seafood, insects, and the flesh of any other animal). It may also include abstaining from eating all by-products of animal slaughter.

Vegetarianism may be adopted for various reasons. Many people object to eating meat out of respect for sentient animal 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, taste-related, or relate to other personal preferences.

There are many variations of the vegetarian diet: 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. As the strictest of vegetarian diets, a vegan diet excludes all animal products, and can be accompanied by abstention from the use of animal-derived products, such as leather shoes.

Vegetarian diets pose some difficulties. For vitamin B₁₂, depending on the presence or absence of eggs and dairy products in the diet or other reliable B₁₂ sources, vegetarians may incur a nutritional deficiency. Packaged and processed foods may contain minor quantities of animal ingredients. While some vegetarians scrutinize product labels for such ingredients, others do not object to consuming them, or are unaware of their presence.