For the military definition of sloop see: Sloop-of-war.For the open learning project see: SLOOP Project.A sloop (from Dutch sloep, in turn from French chaloupe) is a sailing boat with a single mast and a fore-and-aft rig. A sloop has only one head-sail: if a vessel has two or more head-sails, the term 'cutter' is used, and its mast may be set further aft than on a sloop.