A word square is a special case of acrostic. It consists of a set of words, all having the same number of letters as the total number of words (the "order" of the square); when the words are written out in a square grid horizontally, the same set of words can be read vertically. For example:
| 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 magic square, though apart from the fact that both use square grids there is no real connection between the two.
