潟 means 'lagoon'

Land encircles water in various ways, and each essay in this collection spotlights a different shape of that sort: (1) an elongated body of water that's parallel to the coast and set off by islands or reefs, (2) a narrow place where the sea comes a long way into the land, (3) a circular atoll that is the rim of an extinct underwater volcano, and (4) a portion of ocean partly enclosed by land. These essays focus on famous places (e.g., Niigata, Edo, and Taiwan), explaining how those names connect to certain bodies of water.