The term "Atlantic Canada" refers to the provinces of Nova Scotia, New Brunswick, Prince Edward Island, and Newfoundland: the region of Canada east of Quebec and bordered by the Atlantic Ocean. The settlements in Atlantic Canada are among the oldest European settlements in North America, when French and English ships would sail to Canada to fish.
The term is only really used by people "from away", as no one from Newfoundland would ever want to be lumped in with a Prince Edward Islander, and vice versa. Economic growth in the four Atlantic provinces is rather sluggish, compared to the rest of Canada. The cod stocks have been over-fished, the USA is involved in a trade dispute over softwood lumber, people are moving away for better jobs. The governments of the Atlantic provinces are trying to get involved in off-shore oil and gas exploration, and to bring high-tech companies to the region with favourable tax conditions.
At the request of a pedantic noder, I would like to point out that Labrador is indeed part of Atlantic Canada, being a part of Newfoundland. Additionally, Atlantic Canada is also the site of old Viking settlements, recently rediscovered. Thank you.