This extremely rare female perineal piercing sits half way between where a fourchette would be located and an anal piercing would be located. The female guiche is placed across the perineum (ie. running "from leg to leg" rather than front to back (which would be an anal-to-vaginal piercing in most cases).
Naturally, care must be taken during healing to avoid contaminating the piercing, and not all women have anatomy suited to it at all. The first published examples of this piercing were done by Shane Munce who also chose the name (although it has almost certainly been done before).