The "Fourchette" is also a relatively rare female genital piercing of the posterior fourchette that bmezine.com's glossary defines as a "rear labial piercing". There seems to be some debate in the question/answer department (QOD) about the type of piercing/jewellery (curved barbell vs surface piercing) appropriate for this procedure. A high rejection rate is also mentioned.
SOURCES
http://www.bmezine.com/pierce/10-female/other/index.html photograpshs of female genitalia piercings
http://www.bmezine.com/qod3/ (search on "fourchette" these are questions answered by the body modification ezine volunteers)
http://www.bmezine.com/qlossary
thanks to
mkb for pointing out the "Fourchette" piercing and guiding me in finding references.