What is a "roller"?

[Amateria]

I've gotten to a point where certain contracts are requiring use of a "roller", but I cannot figure out what a roller is supposed to be. Nothing in any of the mower descriptions, or parameters, in the shop mentions anything about a roller and I don't know where else to look. If, for some reason, it's useful to see what the contract says, you can see it here[imgur.com].

[Mateo]

It's an attachment on the back of the mower that stripes the grass. It's available to the two Scag zero-turns. Not sure on any of the others.