what does it mean when a washer needs to be put back on its base?

I am thinking of buying a used washer and dryer from someone and they told me that the washer is off its base and it needs to be put back on. I have no idea what this means and am wondering if it is fixable and if it will work after this is done to it. I don't want to pay the $50 for the pair if i haveto pay to fix the washer and it won't work.
Is this fixable and if so what would the appproximate cost be?