A: The term "New Atheist" is generally applied to three main authors and those who share their beliefs and methods -- Richard Dawkins ("The God Delusion"), Sam Harris ("Letter to a Christian Nation") and Christopher Hitchens ("God is Not Great"). Essentially, it refers to an atheist who aggressively advocates for the virtues of a godless society and argues that religious belief of any type should be subjected to the same skeptical inquiry as any other subject, rather than being accorded a special and hallowed place in the public discourse.
Most of those to whom it is applied deplore the term, because there isn't anything "new" about being an aggressive advocate for atheism and against religion (Bertrand Russell's "Why I Am Not a Christian" from 1927, anyone?). What is new is the broad public appeal these authors have achieved, with all of the books referenced above making the New York Times' Best Seller list within a relatively short time span. I suspect it is this commercial and popular success that led to the impulse to come up with a label for them.
I think a more useful delineation would be the one recommended (tongue in cheek) by C.L. Hanson, as "mean atheists" and "nice atheists":
The difference between the mean atheists and the nice atheists is that the mean atheists think that religion is ninety-nine parts pure stupidity mixed with one part lying, opportunistic con artists. And they want to tell that to religious people whenever they're asked to "respect" someone's faith.
The nice atheists, by contrast, believe that religion is more complicated than the stupidity-plus-con-artists model and/or that we should at least make an effort to get along with religious people.
The fight between the two groups is this: When the mean atheists and the nice atheists get together, it's not so much that it annoys the mean atheists to be asked to play nice. It's more that they just want to be able to call the nice atheists names like "sniveling milquetoast" and the like. Y'know, while they're at it. Because when it comes right down to it, the mean atheists just want to have fun.