Rogue waves are the subject of an interesting explanation here, by Steve Lyon at the Weather Channel:

First the definition of a “rogue wave” is, in a nut shell: a freak wave, monster wave, killer wave, extreme wave that is large and spontaneous on the ocean surface. Just the name rogue insights all kinds of persona, specifically a deceitful and unreliable scoundrel!

Wow, how can an oceanographic phenomenon appear to be such a villain, an unexpected freak event of nature? It definitely is not that, rather it is a part of the natural ocean wave spectrum and can be expected at any beach at any time.

OK, beaches receive rogue waves with some frequency. But what about those really big rogue waves we read about in The Perfect Storm? As the wikipedia entry on rogue waves says,

for centuries maritime folklore told of the existence of vastly more massive waves — veritable monsters up to 30 meters (98 ft) in height (approximately the height of a 10-story building) — that could appear without warning in mid-ocean, against the prevailing current and wave direction, and often in perfectly clear weather. Such waves were said to consist of an almost vertical wall of water preceded by a trough so deep that it was referred to as a “hole in the sea”; a ship encountering a wave of such magnitude would be unlikely to survive the tremendous pressures of up to 980 kPa (142 psi)[citation needed] exerted by the weight of the breaking water, and would almost certainly be sunk in a matter of minutes.

Many years of research have confirmed that waves of up to 35 meters (110 ft) in height are much more common than mathematical probability theory would predict using a Rayleigh distribution of wave heights.