A legal position on a Rubik's cube of any size means that it can solved by the normal twisting of the faces. An illegal position
would be one that cannot be solved as such. For example if you take your cube apart and put the pieces back together wrong. From an illegal position you
will never be able to solve your cube by normally twisting the faces.
An example of an illegal position would be to have your entire cube solved except for only one of the corners was rotated clockwise or
counter-clockwise. So if my solution doesn't work for you it might mean that your cube needs to be disassembled and reassembled correctly. If you need to
disassemble your cube then click here.