Rogue Waves, also known as freak waves, monster waves, extreme waves or hundred year waves, are relatively large and spontaneous ocean surface waves that are a threat even to large ships and ocean liners. In oceanography, they are more precisely defined as waves whose height is more than twice the significant wave height (SWH), which is itself defined as the mean of the largest third of waves in a wave record. Therefore Rogue Waves are not necessarily the biggest waves found at sea, they are, rather, surprisingly large waves for a given sea state. A 6-metre (20 ft) wave, such as the one that probably caused the loss of the RV Ballena in Southern California, was a Rogue Wave that occurred in a rather calm sea state. Such a wave is nevertheless very small compared to the largest waves recorded by instrumented buoys, with 17.2 m (56 ft) significant wave height.   Wikipedia