In
windsurfing, a board shorter than 3 metres and less in volume than 150 litres. Generally used for
planing.
At the volume twice the weight of a sailor, shortboards are already quite tricky to maintain balance on without the pull of the sail. Advanced wave or race shortboards, though, can be as small as 70 litres, meaning they can not sustain the weight of the sailor with the rig. These are called sinkers, are meant to be used only in the planing conditions, and are mounted using the waterstart technique.
Shortboards have a fin at the end, but never a daggerboard.