Diet and food restrictions can be a pretty personal choice, one that people make for a variety of reasons. So if you're wondering what your neighbor/coworker/crush really means when they say they're a vegetarian, here's what foods they may be avoiding (or not).
Vegetarians, according to the Vegetarian Resource Group, "do not eat meat, fish, and poultry." That means some vegetarians avoid meat and fish in any form, including dishes made with chicken stock, cheese made with animal rennet, foods made with fish sauce and candies or sweets made with gelatin. Other animal products, like milk, honey and eggs, fall within a vegetarian diet for many people.
People choose to eat vegetarian diets for different reasons. Some do it for ideological reasons, some for nutrition, some people just straight up don't like the taste of meat.
Of course, different vegetarians follow different rules. Some people may choose to avoid meat but feel comfortable eating cheeses made using rennet, some vegetarians may even be fine with soup made from animal stock — so before you cook a meal for your vegetarian friend, ask them about their specific food choices.
A vegan diet means something different — according to Vegan Action, a vegan "chooses to avoid using or consuming animal products. While vegetarians choose not to use flesh foods, vegans also avoid dairy and eggs, as well as fur, leather, wool, down, and cosmetics or chemical products tested on animals." That means that cheese, honey and anything made with egg wouldn't be part of a vegan diet.
A pescetarian is a vegetarian who includes fish and fish products in their diet, and a flexitarian is basically just someone who tries to have a mostly plant-based diet but may eat some animal products, including meat. A good rule for if you're trying to figure out whether your vegetarian friend does or doesn't eat a certain food, just ask them politely.