lacto-ovo-vegetarian: A vegetarian whose diet includes dairy products and eggs.
This term is a misnomer used by vegans, to draw attention to the fact that animal products are being consumed. Traditionally, vegetarian means one who abstains from eating meat, and only meat. Lacto-ovo-vegetarian (alternately, ovo-lacto-vegetarian) is rather redundant.
Sometimes, this terminology is used by people who want to draw attention to the fact that they do not consume eggs or milk, claiming that they are lacto-vegetarian, or ovo-vegetarian. This is an unfortunate example of vegetarian one-up-manship, resulting in people like militant vegans.
For many, the choice to be vegetarian is important for what they choose to omit, not what they choose to include. Furthermore, this sort of terminology starts to break down if we extend it to carno-lacto-ovo-vegetarianism, which is, in fact, the traditional diet of humans, which deserves no special name.
Lacto-ovo-vegan might make more sense in that it would mean "milk, plus eggs, plus non-animal products", but it would dilute the meaning of "vegan", and would just be a long-winded alternative for "vegetarian". The English language has a word for almost everything, why not use the proper words?