Question

What is the Latin square?

Answer

The Latin square is a square array of numbers or letters in which each number or letter appears once in every row and column. For example $\begin{array}{c}\begin{array}{cccc}1& 2& 3& 4\\ 4& 3& 2& 1\\ 3& 1& 4& 2\\ 2& 4& 1& 3\end{array}\mathrm{ \; but\; not\; }\begin{array}{cccc}p& q& r& s\\ q& r& s& p\\ r& q& p& s\\ s& p& r& q\end{array}\end{array}$