Figging is the act of inserting something into the body that will cause a stinging, burning sensation.
The word is likely to be a derivative of "feague", the practice during Victorian times of putting a piece of peeled ginger into a horse's anus to make it appear more sprightly and hold its tail up (for shows and selling). (See the article in a general encyclopaedia.)
Mostly, figging is still used to mean putting a peeled, shaped piece of ginger root (fig) into an anus, but in a BDSM context the anus would be that of a sub. Sometimes 'figging' is used to refer to a pervertable other than ginger (for example nettles) and also to cover the insertion into the vagina, although it may be incorrect to consider these as figging.
For those with masochistic tendencies, the painful sensation can be very erotic. The ginger root is skinned and may also be carved into the shape of a butt plug. Inserting ginger into a healthy anus for even quite lengthy periods should cause no physical damage.
Figging can be used as part of effective physical punishment. If the sub is made to tighten his/her buttocks with a fig inside the anus, the sensation becomes more intense: thus they will usually try to relax those muscles. This provides a good target for caning or spanking, which will often cause the sub to clench his/her backside, which will immediately increase the feeling of heat and pain, thus causing them to want to un-clench. And so the fun continues...
Victorian texts on the proper treatment of recalcitrant wives included the instructions for figging as it was considered that a spanking should be received on relaxed buttocks and this was seen as one way to train them to receive the spanking properly.
Other uses for ginger
Apart from, or together with, frigging, ginger pieces or juice from crushed ginger can be inserted in the vagina or applied to the clitoris or male genitals. Care should be taken here, especially with juice, as the genitals are much more sensitive.