A Latin square is an n X n array filled with n different symbols each occurring only once in each row and once in each column, like a Sudoku puzzle. A Latin square is said to be regular if both its rows and its columns are in the same order, as in a regular word square.
"Regular Latin Word Squares,"
Word Ways: Vol. 50
, Article 14.
Available at: http://digitalcommons.butler.edu/wordways/vol50/iss2/14