The East Coast of the United States, is the Atlantic coastline of the United States. It is also called the "Eastern Seaboard" or "Atlantic Seaboard".
The coastal states are the farthest eastern states of the United States. These states touch the Atlantic Ocean all the way up to Canada. Sometimes people use it to mean only the Northeastern United States. Other times they mean the thirteen original states plus Maine, Washington, D.C. and Florida.