The term MEDIUM'S BOARD can be solved by the crossword solution of OUIJA, which is a board game that is used to communicate with spirits. It was first invented in the late 19th century and has been popular ever since. The game involves a board with letters, numbers, and symbols, as well as a planchette, which is a small device used to point to the letters on the board. Players place their hands on the planchette and ask questions, and the spirits are believed to answer by moving the planchette to the correct letters.