Lido deck

A lido (/ˈliːdoʊ/ LEE-doh, /ˈlaɪdoʊ/ LY-doh) is a public outdoor swimming pool and surrounding facilities, or part of a beach where people can swim, lie in the sun, or participate in water sports. On a cruise ship or ocean liner, the deck with outdoor pools and surrounding facilities is often designated the lido deck.

Lido is an Italian word for "beach" and forms part of the place name of several Italian seaside towns known for their beach, e.g., Lido di Venezia, the barrier beach enclosing the Venetian Lagoon. Possibly, the term found its way into English from English visitors returning from the Lido di Venezia, where sea-bathing took place from the late 19th century.

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Wikipedia