There are no absolutes... Like I mentioned with the insects, everyone eats SOME bugs. Especially if you are eating organic, because that implies a slight increase in bug matter because of the avoidance of pesticides.
Here are my definitions, based on my experience:
Vegetarian: One who makes an honest and concerted effort not to eat things cut off the bodies of dead animals. No fish, no 'meat', no poultry, etc. Ovo-Lacto Vegetarians eat eggs and dairy. Ovo = just eggs, Lacto = just dairy. I am ovo-lacto vegetarian.
Vegan: One who makes an honest and concerted effort not to eat animal products of any kind, or use things made from animal products.
Pescetarian: This will be a handy one to some of you! Someone who would fit the category of Vegetarian, but who eats fish. My girlfriend is this.
Some other interesting categories:
Janite Buddhists: People who make an honest and concerted effort not to eat anything that harms or kills the originating lifeform. This means fruit, free-range eggs and dairy, but no carrots (since it kills the plant). They even sweep the ground in front of them as they walk to prevent stepping on bugs. More strict than veganism in many ways, but less in others (like free-range eggs and dairy being OK). Purely ethically based. If you meet one of these people, give them mad props.
Raw food: Any of the above categories can also be 'raw only'. Again, an honest and concerted effort to eat uncooked foods only is what distinguishes.
Hunter/gatherer: People who only eat meats or animal products that they caught themselves. I know several people who are basically vegan with the exception of their semi-regular bowhunting trips that yield the only meat they will eat during the year.
Etc. Etc. Etc....
The point of all these designations is that they are for convenience only. There are as many different diets as there are people on Earth. I think the thing that makes people fit these categories is the effort they put into it, and their honest intents and desires to eat a certain way. If a vegan accidentally gets some honey in their muffin, I won't revoke their 'vegan' status, as long as they are doing what they can to prevent it from happening.
peace,
sam