For most of the meat-eating community, the many variations on vegetarianism can get confusing, especially when they are inviting vegetarians to dinner. The vegetarian community has developed specific titles for different kinds of vegetarians, ranging from pure to pesco. If you are ever in doubt, always ask. Most people do not mind answering questions about their dietary needs, and are in fact grateful for the thought.
As a general rule, a vegetarian is someone who eats a voluntarily restricted diet out of ethical or health concerns. Everyone has different personal boundaries. For example, a person may be willing to eat eggs from free-range chickens, but not from battery hens, or may prefer organic to conventional milk. Usually these preferences are expressed, especially when a person is invited to dinner, as he or she has a vested interest in having something to eat. Cooking for vegetarians is actually remarkably easy, especially when cooks start to include ethnic cuisines, such as food from India and Africa.
The most strict type of vegetarian is a vegan, sometimes called a strict or pure vegetarian. A vegan does not eat any animal products at all. When inviting a vegan over to dinner, avoid meat, eggs, dairy, honey, and any food products which are derived from animals. Some vegans find the consumption of honey and other insect-derived ingredients acceptable, but they will appreciate cooks who err on the side of caution.
The most common vegetarians are those who do not eat meat, but will eat animal products. They usually simply call themselves vegetarians. In nations where “vegetarian” means “vegan,” they may distinguish themselves as lacto-ovo, or "milk-egg" vegetarians. Some people eat eggs but not milk, or vice versa, and they will usually indicate this. Avoid serving meat of any kind to these people, but animal products are usually acceptable.
Pesco vegetarians eat fish, but not red meat. In individual cases, pescos may be willing to eat fowl as well. Some members of the community feel that people who eat fish aren't truly vegetarians, since fish are living animals. Those who do eat fish may also avoid fatty fish like tuna and swordfish out of concern for mercury contamination. Beyond pesco vegetarianism, most people will eat almost anything, although specific meats may be restricted for religious or personal reasons. In these instances, someone will usually identify an unwillingness to eat pork, beef, shellfish, or other foods they try to refrain from consuming.
A final category includes those who will not purchase animal products, but will eat them if they are going to be discarded. These people are usually called “freegans,” a portmanteau of “free” and “vegan.” Freegans accept that other people eat animal products, and they would prefer to see them used rather than wasted. Some religious sects are also freegan, meaning that they prefer not to eat animal products, but they will eat them if offered.