means The land along the edge of the sea, especially a coastal area visited for holidays, swimming, and salty air.

from A plain marriage of two old Germanic words: 'sea' (Old English 'sǣ') and 'side' (Old English 'sīde,' meaning edge or border). The compound simply names the side where the sea begins — though its flavour of buckets, deckchairs and promenades is largely a later gift of the holiday-going centuries.