The NDP (New Democratic Party) is a far-left, essentially socialist party that gets about 10% to 20% of the vote. Its support tends to be concentrated in large cities and in the Maritime provinces. They essentially steal votes from the Liberals, but in some Ridings (districts) they get the most votes.
I'm not sure where you're getting your numbers from, but there is little NDP support in the Maritimes. Of the total number of seats in the Atlantic Provinces (32), which includes Newfoundland, only 3 were won by the NDP.