A Little Introduction About Cue Cards
Not everyone has a good aptitude for remembering the words of a script or speech or song... and that's where Cue Cards come in. They are also known as note cards and the newer incarnation called a tellaprompter*.
They "are cards with words written on them that help actors and speakers remember what they have to say. They are typically used in television broadcasts where they can be held off-camera and are unseen by the audience. Cue cards have largely fallen out of favor with modern broadcasters, being replaced by the teleprompter, but many TV shows, including sitcoms and reality shows, still use cue cards due to their mobility, as a teleprompter only allows the actor or broadcaster to look directly into the camera." (wickapedia)
Also used in some talk shows and game shows recorded before a live audience are electronic signs with the word "Applause" or "Laughter" on them. The producers of the show can cause the sign to light up or flash and thereby tell the audience to do so.