A crossword puzzle is a two-dimensional grid of boxes, some of which are blackened out, such that the result is several subsets of rows and columns into which the solver puts words that fit together. The words come from clues that are given to the solver.
boatloadpuzzles.com/playcrossword
The premise of this class is describing a word search; where you have a two-dimensional array of letters, some of which form words either up, down, left or right. Some word searches also form words diagonally.