Coastlines are formed through erosion and sediment deposition processes. They are shaped by sea level changes and the interaction between land and ocean. A coastline includes beaches, cliffs, and other landforms at the boundary between land and sea. Coastal zones experience continuous change from tidal movements and ocean interactions with the shore. Erosional landforms like sea cliffs and arches form through destructive wave energy, while depositional landforms like beaches and barrier islands are built up from sediment deposition.