Sentence:  In winds above 10 knots we usually run wing-and-wing with our 100 percent lapper set on a whisker pole opposite the mainsail. As the wind drops, we get out the <WSD>drifter</WSD> and set it flying to leeward (Fig. 1). 
Meaning of the word marked with <WSD> tags:  A type of lightweight sail used in light winds like a spinnaker.