User blog comment:Kinshi57/Sci-Fi or Brutal Death?/@comment-4244032-20111027010821/@comment-4132342-20111027214719

By grinding they probably mean grinding for badges or points on this website, ie. Just farming for them, working in weird ways to get them. That's the best I can explain it, but it's also called grinding when you fight random enemies for experience for awhile to level up in RPGs, so same concept, kind of.

As far as human grinding goes...ask your mother.