* West Egg: Where Jay Gatsby lives and throws his lavish parties. It's described as being across the bay from New York City and more "fashionable" than the other side of the island.
* East Egg: Where Daisy Buchanan and Tom Buchanan live. It's depicted as being closer to New York City and more "established" than West Egg.
While the book doesn't explicitly name the specific towns on Long Island, it's generally understood that West Egg is based on the real-life area of Great Neck, and East Egg is based on Sands Point and other towns on the North Shore.