Latin Square
<p >In <a href="http://en.wikipedia.org/wiki/Combinatorial_design" title="Combinatorial design" >combinatorics</a> and in <a href="http://en.wikipedia.org/wiki/Design_of_experiments" title="Design of experiments" >experimental design</a>, a <b>Latin square</b> is an <i>n</i> × <i>n</i> array filled with <i>n</i> different symbols, each occurring exactly once in each row and exactly once in each column. Here is an example:</p>
<table class="wikitable" ><tbody>
<tr>
<td >A</td>
<td >B</td>
<td >C</td>
</tr>
<tr>
<td >C</td>
<td >A</td>
<td >B</td>
</tr>
<tr>
<td >B</td>
<td >C</td>
<td >A</td>
</tr>
</tbody></table>
<p >The name "Latin square" is motivated by mathematical papers by <a href="http://en.wikipedia.org/wiki/Leonhard_Euler" title="Leonhard Euler" >Leonhard Euler</a>, who used <a href="http://en.wikipedia.org/wiki/Latin" title="Latin" >Latin</a> characters as symbols. Of course, other symbols can be used instead of Latin letters: in the above example, the alphabetic sequence A, B, C can be replaced by the integer sequence 1, 2, 3.</p>