Jigsaw puzzles have lots of different shaped pieces that all fit together without gaps. Most puzzle pieces have four sides with buttons added on to them or cut out of them similar to these:
Imagine that the puzzle pieces are roughly a rectangular shape and all the same size. They can have a button added on or taken out of the middle of any side.
How many different puzzle pieces could there be?
Have you got them all? Have you got any that are really the same?
Have you remembered the straight edges?
What about the corner pieces?