Barracks what i think he might mean is just lube + dirt build up on his cassette. looks like grease.. but isn't.

In between full break downs i take a metal tooth cleaning thing like they scrape with at the dentist and scrape off the gunk from between the cogs. I also do that to the sides of the Rear derailleur pulleys where stuff usually gathers up.

When it starts looking real grungy I take the cassette off the wheel, dissemble and clean it with Simple Green.