A lacto-ovo vegetarian is a vegetarian who does not eat beef, pork, poultry, fish, shellfish or animal flesh of any kind, but is willing to consume cheese, butter, yogurt and eggs. Lacto- means "milk" and ovo- means "egg".
In the Western world lacto-ovo vegetarians are the most common type of vegetarian. Generally speaking, when one uses the term vegetarian a lacto-ovo vegetarian is assumed. Lacto-ovo vegetarians are often well-catered to in restaurants and shops, especially in Europe and metropolitan cities in North America.
Some lacto-ovo vegetarians who are motivated by ethical reasons but some, like Sue, are motivated by the fact she is allergic to meat, fish, chicken... any meat product. In contrast, a vegetarian who consumes no animal products is called a vegan.