Dinghy – A small sailboat usually under 20 feet long and open for most of its length.
Keel – A fixed appendage on the bottom of the hull that provides sideways resistance needed to counter the force of the wind on the sails. The keel also carries ballast, usually iron or lead, the weight of which counteracts the force of the wind that causes a sailboat to heel, or lean over.
Hull – The watertight structural shell of a boat.
Bow – The forward part of a boat
Stern – The aft part of the boat. 
Transom – The more or less flat surface that closes the hull at the stern
Rudder – The sailboat is steered by a fin-shaped appendage attached beneath the boat toward the stern which can berotated to change the angle at which the water strikes it. Water must flow past the rudder in order fo rit to work so it will not turn the boat while at rest.

The rudder is controlled by a wheel or a tiller at the helm of the boat. The person steering the boat is the helmsman.
Cockpit – The area of the boat, usually recessed into the deck, from which the boat is steered and sailed.
Deck – The generally horizontal surface that encloses the top of the hull.
Companionway – The entrance from the cockpit or deck to the cabin.
Stanchion – A metal post that supports lifelines.
Lifeline – A wire supported on stanchions around the perimeter of the deck to prevent crew from falling overboard.
Pulpit – A guardrail at the bow or stern of a boat to which (usually) the lifelines are connected.