In someboats and ships, atransom is the aft transverse surface of the hull that forms thestern of a vessel. Historically, they are a development from thecanoe 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 thewaterline, 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 thebow. A reverse transom is angled from thewaterline forwards.^[3]

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

The term was used as far back asMiddle English in the 1300s, having come fromLatintransversus (transverse) viaOld Frenchtraversain (set crosswise).^[1][5]

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  Flat transom on a dinghy with mount points for arudder.
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  TheBermuda cedar transom of theSpirit of Bermuda
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  Raked transom with rudder mount points.
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  Reverse transom with rudder mounted under thehull.
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  Transom-mountedoutboard 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).