1) I'd say "being sentient" is a good definition for that. What exactly is sentient is left open to interpretation a bit, but I know big animals are, and I know plants aren't.
2) Eating meat is immoral, animals can't reason about morality, therefore they do whatever they do. Morality is the domain of beings intelligent enough to think about it. I consider killing animals immoral. That said, I do eat meat, because it's so tasty, in full conscience that I am immoral.
If you are so inclined, you could try being a weekday vegetarian - http://www.ted.com/talks/graham_hill_weekday_vegetarian.html. For me, the two hardest things, when finally quitting eating meat a year ago, were convincing everybody around me that was serious about it, and finding alternative foods. I still occasionally eat fish. I try to justify it to myself as fish being of lesser intelligence and sentience.
2) Eating meat is immoral, animals can't reason about morality, therefore they do whatever they do. Morality is the domain of beings intelligent enough to think about it. I consider killing animals immoral. That said, I do eat meat, because it's so tasty, in full conscience that I am immoral.