First a Vegan is rarely ever a enviromentalist term, though many do believe by not eating animals you are helping the enviroment, because food animals do require more land, water and energy to produce then vegetables, Veganism is more about animal rights. Vegans do not eat any product that comes from an animal, this includes byproducts that come from the death of an animal such as gelatin, and byproducts that do not result from the death of an animal such as eggs, dairy or honey.
Vegans are different in the fact that they also on the whole do not use any unedible products that come from animals even one's that do not result in the animals death such as wool and feathers. This includes animal products in clothing, bath and body and in other areas of their lives.
Though this is a sticking point you will sometimes find Vegans who will wear or use recycled animal products such as animal fibers and leather. Many do this as a way to be more enviromentally friendly. Also because they have pieces from before they became Vegan and think its disrepectful to throw away. This is not common but does occur amoung some Vegans.
What is NOT Vegan;
Meat (soild pieces, stocks, bone etc)
Tallow (Tallowate- Animal Fat in Soap)
Red #4 (from crushed beatles)
Dairy (the straight milk or products that include any types of animal milks)
Honey (includes Beeswax)
Processed Sugar -(most White Sugar and some Brown Sugars are processed with Bone Carr. Beet Root Sugars, Raw Sugar, Organic Sugar and some White Sugars are differently processed so are Vegan)
Beer (some beers are clarified with Islinglass, which comes from a Fishes Swim Bladder)
Wine- (Some wines are clarified with eggs or gelatin)
Chocolate- (Since most chocolates are processed with milk or white sugars most Vegans only work with pure Chocolates or from certain companies who use Vegan Sugars)
Wool or any other types of animal fiber
Fur or any sort
This is a basic list to give you some idea of what products are not exceptable.
I also wanted to take a moment to say that KOSHER does not always mean Vegan and vice versus. Kosher is a term for a product that has been made in a way that is safe for consumption by a Rabbi for someone of the Jewish faith. Jews eat meat, though they have strict rules about food this does not mean that animal products are not in the item because it is Kosher. In fact Kosher Gelatin is just standard gelatin that has been prepared by the Jewish Kosher laws. It is still from an animal. Also because of the lack of a Rabbi at the foods production, unless marked Vegan foods are not all Kosher either.
Organic also does not mean Vegan. As I wrote much earlier the laws are very strict about what organic is and that is that the food must be produced in a way without pesticides or other chemicals, any grower must prove their standing to use the term organic and have a certain rate of Organic foods in a product to claim Organic. Because meat, honey/beeswax and other products can be Organic this does not mean that they are Vegan. This term is regarding the way a product is grown and produced not if it contains animal products.
This is just a small bit about Veganism and I hope it helps you to understand what they stand for, as well as to be able to understand them as a Market. As I see more people turning towards the terms I really hope that people understand that for these people this is more then a lifestyle it is a belief system and hope that with this knowledge you will be better able to understand their choices.