Not my field, but here are some references:

cul-de-sac vaginal
nm.
fornix of vagina [MED]
http://dictionnaire.reverso.net/francais-anglais/cul-de-sac

Definition of Vaginal fornix
Vaginal fornix: The anterior (front) and posterior (back) recesses into which the upper vagina is divided. These vaultlike recesses are formed by protrusion of the cervix into the vagina. The fornix uteri is also known as the fornix vaginae (or the vaginal fornices) and the uterine fornices.
http://www.granddictionnaire.com

And a picture:
http://www.anat-jg.com/PeritoineSous/OGF/Vagin.Vulve.htm

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Note added at 4 hrs (2012-01-29 00:17:22 GMT)
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Picture in English on this Wiki: http://en.wikipedia.org/wiki/Vaginal_fornix

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Note added at 6 hrs (2012-01-29 02:06:22 GMT)
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Oops, maybe not "vaginal"! Could it be for men? In which case, just:

fornix ;-)

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Note added at 10 days (2012-02-07 20:18:07 GMT) Post-grading
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@ Bashiqa: You're welcome and thank you too.