Rolex invented the first truly waterproof case, which he called the “Oyster,” a name Hans Wilsdorf came up with after trying to pry open a really stubborn oyster shell.
The “Perpetual” part came in 1933, when Rolex rolled out the first reliable self-winding watch, and called it the Oyster Perpetual. Perpetual, meaning it goes on and on and on…
“Oyster” means waterproof.
“Perpetual” means it self winding or automatic.