In archi-decorative terminology, these are used. A torus is a protruding moulding. It can be of different shapes, elongated, pear-shaped, pointed, etc. , like a ball on a stick beyond the face of the structure, or may simply be a semicircular "bump" along the face.

A gorge is a recessed moulding, usually semicircular.

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Note added at 45 mins (2007-09-11 21:46:24 GMT)
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http://www.bamboofloorings.info/9/bamboo-flooring-moldings/

www.goodbros.co.uk/skirting_mouldings.html

Gorge: a hollow moulding. GRP: glass reinforced plastic. ...
www.plasterarc.net/essay/essay/GleesonGH.html

A deep concave molding, or gorge, especially at the base of a column. ...
www.stoneonline.com.cn/glossary.html

gorge – 1 In some orders of columnar architecture, a narrow band around the shaft, near the top ... 2. A cavetto or hollow molding ...
Also "scotia"
scotia – A deep concave molding, edp. one at the base of a column in Classical architecture. Also called a gorge, trochilus

[Dict. of Arch. & Const, Cyril Harris, McGHill]


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Note added at 1 hr (2007-09-11 22:51:20 GMT)
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All the illustrations I have found of a French "gorge" show a semicircular concave moulding. I have not been able to find the same in English. A scotia is an "inclined ellipse" (Greek) or "struck from two centres on a common radial line" (Roman) (variable curvature). A cavetto is a quarter of an ellipse (Greek) or of a quadrant (Roman) [Mitchell].

The term "gorge" in French seems to be too precisely defined to be anything else, such as a quirk.