Who eats what?
Vegetarians don't eat any meat, fish, seafood or animal by-products such as gelatine, but the majority of vegetarians do eat some animal products, mainly milk, cheese (made with vegetarian rennet) and eggs. Some people may eat different combinations of these foods, so for instance some may have milk but not eggs, a few might eat fish but not meat.
However, vegans don't eat any foods of animal origin. This includes meat, fish and dairy foods, and also honey.

What nutrients should I be concerned about?
If you are a vegetarian (or vegan), you need to make sure you're getting enough protein and iron and if you are vegan you need to make sure you are getting enough vitamin B12.