A word square is a type of acrostic. It consists of a set of words written out in a square grid, such that the same words can be read both horizontally and vertically. The number of words, which is equal to the number of letters in each word, is known as the "order" of the square. For example, this is an order 5 square:
| H E A R T |
| E M B E R |
| A B U S E |
| R E S I N |
| T R E N D |
A popular puzzle dating well into ancient times, the word square is sometimes compared to the numerical magic square, though apart from the fact that both use square grids there is no real connection between the two.