I recently met a student online named Alex Leavitt. Alex is one of the new generation of scholars in the US studying otaku culture, and I couldn't be more pleased, as we desperately need more serious investigations of otakudom (from all angles).
On his blog, Alex posted some interesting thoughts on the meaning of 'anime', especially in light of works like Kunio Kato's La Maison en Petit Cubes, which recently won the Academy award for 'Short Film (Animated)': Reflections on Anime: Animation and the Academy.
Here's my comment on his post:
Thanks for sharing your thoughts. I generally define anime as the following:
Animation created (primarily) in Japan by Japanese creators for (primarily) Japanese audiences.
I use that definition because it's useful to me as both a fan and scholar, allowing me to delineate the aspects of 'anime' (re: context, production, and reception) which I am most interested in. In the end, the word 'anime' is just a container for whatever concepts we want it to hold.
That said, I certainly enjoy (and find important) many things that fall outside of 'anime' as strictly defined above.
In another sense, my definition might be considered less strict than most since it places less emphasis on specific anime styles and genres, allowing us to recognize as anime historically important but stylistically distinct titles (such as Tezuka works, as you mentioned), along with modern Japanese works such as La Maison en Petit Cubes.
Below is a video filmed by Cameron Williamson of AniLogTV, asking attendees of Anime Punch 2008 "What is Anime?" (I'm at the end of the video)