A sloop is a sailboat with a single mast typically having only one headsail in front of the mast and one mainsail aft of (behind) the mast. Such an arrangement is called a fore-and-aft rig, and can be rigged as a Bermuda rig with triangular sails fore and aft, or as a gaff-rig with triangular foresail(s) and a gaff rigged mainsail. Sailboats can be classified according to type of rig, and so a sailboat may be a sloop, catboat, cutter, ketch, yawl, or schooner. A sloop usually has only one headsail, although an exception is the Friendship sloop, which is usually gaff-rigged with a bowsprit and multiple headsails. If the vessel has two or more headsails, the term cutter may be used, especially if the mast is stepped further towards the back of the boat.
When going before the wind, a sloop may carry a square-rigged topsail which will be hung from a topsail yard and be supported from below by a crossjack. This sail often has a large hollow foot, and this foot is sometimes filled with yet another quadrilateral square rigged sail called a "save-all topsail."
The name originates from the Dutch sloep, which is related to the Old English slūpan, to glide. In naval terminology, "sloop-of-war" refers to the purpose of the craft, rather than to the specific size or sail-plan, and thus a sloop should not be confused with a sloop-of-war.
After the cat rig which has only a single sail, the Bermuda rig is the simplest sailing rig configurations. It is the most popular yacht rigging because it is easier to sail with a smaller crew or even single-handed, it is cheaper since it has less hardware than more complex rigs, and it sails well into the wind. A limitation is that when a boat gets over 45 feet in length, the sails become so large that they are difficult to handle, although modern technology is helping with this through the use of electric winches and furling systems.
The headsail can be masthead-rigged or fractional-rigged. On a masthead-rigged sloop, the forestay (on which the headsail is carried) attaches at the top of the mast. On a fractional-rigged sloop, the forestay attaches to the mast at a point below the top. A sloop may use a bowsprit, a spar that projects forward from the bow.