The original place I seen it was on Wikipedia, so far I haven't done any further reading up on it as of yet, but here is the quote from Wiki. . .
I followed Wikipedia's referenced source.
They may be referring to a contract option that was originally offered, which would have presented 6, with options for possible 7th and 8th seasons. TNG was somewhat innovative in that it was distributed via syndication, which was unusual for a dramatic series at the time.