I'm a pescatarian (which means I eat seafood, but no other animals). I know the LITERAL meaning of the word 'vegetarian' means "someone who doesn't eat creatures", but for those of us with 'alternative' dietary choices, it becomes MUCH easier to tell people we're "essentially vegetarian". At least, that's my experience.
I can't even begin to count the number of times I've had this conversation:
me: "I eat fish, but no other meat."
other person: "But you still eat chicken, right?"
me: "No, I don't eat any other creatures besides fish."
other person: "What about pork?"
For me, saying "I'm essentially a vegetarian, except I also eat fish." is a faster way of helping the other person understand my diet. I get to bypass the whole conversation above.
Yes, I know I'm not using the word in the clearest or most concise context, but I'm a fan of arriving at my objective by the quickest and most efficient means possible. If I must leave semantic carnage in my wake, so be it.