In some boats and ships, a transom is the aft transverse surface of the hull that forms the stern of a vessel. Historically, they are a development from the canoe stern (or "double-ender") wherein which both bow and stern are pointed.

Transoms add both strength and width to the stern. They may be flat or curved and they may be vertical, raked forward (known as retroussé), or raked aft.^[1] In small boats and yachts, this flat termination of the stern is typically above the waterline, but large commercial vessels often exhibit vertical transoms that dip slightly beneath the water.^[2] On cruising boats, a counter stern may be truncated to form a "truncated counter stern", in which there is a part of the stern that approximates a transom.

Although that standard stern transom is typically vertical, they may be raked such that there is an overhang above the water, as at the bow. A reverse transom is angled from the waterline forwards.^[3]

On smaller boats such as dinghies, transoms may be used to support a rudder, outboard motor, or a wind-generator pole. On cruising yachts, the transome may hinge outwards (when at anchor) to form a swimming-cum-access platform, and to provide a lazarette for deck items and leisure toys.^[4]

The term was used as far back as Middle English in the 1300s, having come from Latin transversus (transverse) via Old French traversain (set crosswise).^[1][5]

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  Flat transom on a dinghy with mount points for a rudder.
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  The Bermuda cedar transom of the Spirit of Bermuda
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  Raked transom with rudder mount points.
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  Reverse transom with rudder mounted under the hull.
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  Transom-mounted outboard motor.
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  An Irwin 44 with a fold-down transom.
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  Reverse transom with access platform.
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  Traditional timber construction with horizontal transom members in pale yellow-green (6) and turquoise (7).