A dodger (also known as a spray-hood) is a frame-supported canvas (usually with clear vinyl windows) structure partially protecting a helmsman and other occupants of a sailboat from harsh weather and seas.
It covers part of the cockpit and the entrance (or "companionway") into the interior of the sailboat.
One can usually stand under a dodger and be protected from rain, spray and snow travelling straight down or from the front/fore of the craft.
A similar type of shelter on a boat, without the forward and side protection, is called a Bimini top.
Increased protection for the occupants of the cockpit is possible using a combination of dodgers/bimini tops and dodger extension.