A Graeco-Latin Square is a mathematical arrangement used in experimental design, particularly in statistics. It consists of a square grid where each row and each column contains a unique set of symbols from two different sets, ensuring that each pair of symbols appears exactly once. This structure helps control for variability in experiments. The concept was developed by Leonhard Euler in the 18th century. Graeco-Latin squares are useful in various fields, including agriculture and psychology, as they allow researchers to study the effects of two factors simultaneously while minimizing bias and confounding variables.