The coast also means the land next to the sea, which can also be called the shore, or sea-shore. However, coast is not used to describe where rivers or lakes meet the land - it is only used to describe the sea meeting the land.
If a house is near to the coast we say it is "on the coast". When we talk about a long part of the coast we call it "the coast-line". Sometimes, 'coast' can be part of a place name or the description of a large area. For instance, the East Coast of the United States describes the all of the Eastern side of the United States that is next to the Atlantic Ocean.
Coasts often have many living things living there and provide habitat for many animals and plants.