What is butterfly board in gay sex?

What is butterfly board?

A board, used in SM, that has a hole cut out, to allow for the penis and scrotum to be inserted through.

Definition

A board, used in SM, that has a hole cut out, to allow for the penis and scrotum to be inserted through. Usually a thin piece of wood, or even cardboard, is used. Once inserted, the Dominant will affix the skin of the scrotum, and/or penis to the board, with pins, tacks, nails, or other similar items. Also used in play piercing, where non permanent piercing is done.