Sometimes simply referred to as a "diagramless", the diagramless crossword is similar to an
American crossword except that you are not provided with the locations of the
black squares and the start of each word in the puzzle. Instead, you only get a blank
grid of the appropriate size, information about the
symmetry of the puzzle (which differs from normal crossword symmetry a little more often than in normal
crosswords), and sometimes the location of the start of
1 Across.
Usually, you can expect the following about the grid: It contains no unchecked letters, and no two-letter words. However, diagramless crosswords often have many more black squares than typical crosswords, and often these black squares are structured so that they (or the white squares) form some special shape. GAMES Magazine once printed a set of 4 diagramless crosswords over 4 consecutive issues that were in the shapes of the four suit symbols in a standard deck of cards (note that three of them have left-right symmetry instead of the normal crossword symmetry).
The clues are numbered as they normally would be if you had the normal type of numbered grid. You use the information provided by the numbers together with answers to clues you are able to figure out to reconstruct the grid. For example, you always know the length of 1 Across, because each letter in 1 Across must have a number and a corresponding down entry, and the next across answer starts with the next number. So if the second across answer is 6 Across, 1 Across has 5 letters. (It gets harder after this.)