Skeletons are a type of crossword puzzle, but instead of being given a full puzzle of numbers and squares and simply filling out the answers, you must work out the answers of the numbered clues and create the black and white squares yourself.
In a symmetrical skeleton, when the grid is complete, it will look the same in every direction meaning that you can deduce the positions of more black squares (if not most) right away.
For all skeletons, the numbered clues will always appear in chronological order, from left to right and top to bottom, which can make the positions of other clues easier to place (ie. 13 Down will begin in a square to the right of 12 Down in the same line, or in one of the lines below it — never before.)
Skeleton Crossword blank puzzle
Skeleton Crossword completed puzzle