The "Fourchette" is also a relatively rare female genital piercing of the posterior fourchette that'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 photograpshs of female genitalia piercings (search on "fourchette" these are questions answered by the body modification ezine volunteers)

thanks to mkb for pointing out the "Fourchette" piercing and guiding me in finding references.