Pescatarian is a more recent term and may or may not be considered a degree of
vegetarianism. Pescatarians will eat
fish,
shellfish and
crustacea, but no meat, poultry, game or
slaughter by-products. They are not considered to be a "true" vegetarian, by most vegetarian's standards, but some consider themselves to be. In fact, some vegetarians are rather
hostile to pescatarians. For example, the person who runs Swabe.org says that they can "in no way be seen as adequately adhering to the vegetarian ethic".
Ovo-lacto-pescatarians (or ova-lacto, as I've also seen it) will eat eggs and milk, and those who do make up the majority of the group. Health wise, pescatarians don't have to worry about getting
vitamin B12 as much as straight out vegetarians.
http://tools.healthandage.com/drirene/qa3/qa270062.htm
http://www.swabe.org/veggie.htm
http://www.veggiefiles.com/dir/not_alone/meatheads/88.php