This is for UK English Seaside generally refers to a place on the sea coast or by/at the seaa it refers to the part of a town or place where is is located. Shoreline refers specifically the where the sea meets the land or "the beach". Bank refers to many different things but for this context and comparison it refers to a slope by the sea. Or a place where sand and other natural things are washed/swept up onto a beach to cause a slope or bank 1) seaside. https://www.telegraph.co.uk/culture/photography/9466586/Martin-Parr-on-Britains-best-seaside-towns.html 2) a shoreline http://www.2030palette.org/living-shorelines/ 3) a bank by the river can be sen in the second picture this one was man made https://corporate.thameswater.co.uk/media/News-releases/News-Release---Water-voles-on-the-River-Cole

A seaside is mostly used to describe the area of land near the sea. It's used in a more general sense such as "we spent the month seaside" ("we spent the month near the sea") Bank is the actual land along the edge of a river. I saw a definition describing this as the place you would put your blanket to have a picnic near the river. A shoreline is the "line" where the land meets a large body of water. This can be a lake, river, or an ocean. If you thought of a child drawing a picture, the line they drew of the water would be the "shoreline".