It is if you're Japanese in Japan watching Avatar on Japanese TV.
Discussions like this always hinge on which definition of the word "anime" you choose to use, because there are three separate and distinct English definitions for the term and they partially overlap:
1. The Japanese word for "cartoons"
2. Animation that adheres to a specific set of visual and storytelling styles which nobody seems to be able to define consistently without either ruling out cartoons most people would say, "That's anime" about or ruling in cartoons most people would say, "That's not anime" about.
3. Animation produced in Japan primarily for the consumption of the Japanese market
If you want to use definition #1, then EVERYTHING is anime, but then there's absolutely no point to arguing over whether something "is" or "isn't" anime. If it's animated, it's anime. As a result, this is a boring definition and completely defeats the purpose most people seem to have when they ask, "Is X cartoon an anime?" because the self-evident answer is "Yes" as long as X is actually a cartoon.
Definition #2 is sort of like pornography, in that "I'll know it when I see it," except that (also like pornography) people turn out to have have different definitions of what pornography is. The Sports Illustrated swimsuit issue, Playboy magazine, and those cheapo sexploitation films on Cinemax have all been termed "pornography" by different people, over and above the usual stuff people expect. This usage of "anime" may allow for interminable discussions on Internet message boarRAB, but it is completely useless as a definition for anything.
Definition #3 is the second-easiest to articulate and state definitively if something is or isn't anime. If you want to start talking about common themes or stylistic elements to specific anime, then that's something separate from the definition of the word.
"Anime" is a loan word from Japanese, so the meaning can be different between its original language and its usage in English. "Shampoo" apparently comes from a Hindi verb of "to pound or knead," but that doesn't mean I'm going ask for a good shampooing at a spa and then get annoyed when they start washing my hair instead of giving me a massage.