Zener cards are cards used in testing for psychic abilities, such as clairvoyance. There are 25 Zener cards in a pack, with 5 cards of each design. The 5 designs on the fronts of the cards are a circle, a cross; a five-pointed star in outline form; a square and a trio of vertical wavy lines.
Invented by parapsychologist J.B. Rhine, as an easy statistically measurable way of testing for ESP, according to the scientific method. Rhine named them in honor of his colleague Karl Zener, a perceptual psychologist. Dr. Zener had selected the five designs that would appear on the cards. When Zener cards were first invented in the 1920s, they were shuffled by hand, but Rhine later switched to having a machine shuffle them.