The seashore is the land right where the sea stops — sand, rocks, little pools, the wet ground the water keeps touching. A beach is usually the sandy part you sit on; the seashore can be rocks as well. People also say the shore or the seaside. Seashore is a little quieter and older than beach: you meet it in stories, on signs, and in “a walk along the seashore.” In everyday talk a lot of people just say beach even when they mean the whole edge. You go to the seashore; you do not “do” seashore.