Coastal things are near the ocean. If you like spending time at the beach, you might take a trip to a sunny, coastal vacation spot. Be sure to pack your swimsuit!
You might read phrases like "coastal waters" or "coastal erosion" in an environmental science textbook. The coast is the land that borders an ocean or sea, and the adjective coastal describes things that affect the coast or are located there. Before it meant "edge of the land," coast referred to a body part—specifically, the rib or "flank."