idiot board 
(also idiot card)
noun informal
A board displaying a television script to a speaker as an aid to memory.‘Subterranean Homesick Blues’ plays on the soundtrack, while a flawlessly deadpan Dylan holds up idiot cards with phrases from the lyrics scrawled on them, so you can get the message....
- It's so predictable, you expect idiot cards - LAUGH, FEEL MUSHY, APPLAUD - to flash across the screen.
- With Peter, I was slightly worried because I had heard stories from friends who worked on the Harry Potter films about Richard Harris being [drunk], having to have huge idiot boards and earpieces, and having had temper tantrums.