A sloop is a small versatile sailing ship.
Sloops were single-masted and rigged with a 'fore and aft' sail, and with one jib (staysail) before the mast. They had a long bowsprit and a very shallow draught which led to them being much favoured by pirates because of their manouverability.
Such a sloop is mentioned in the title of a Beach Boys song "Sloop John B".