what word form of 8 x 500 word means

We need much more information before we can even begin to understand what you are trying to do. It might mean 8 articles of 500 words each. It might mean a block of text which is 8 columns and 500 rows containing one word per cell, as in a word list. Please be more specific about where you saw this and what it refers to. Give the whole sentence in which it occurs.