The phrase "provide an piece" regarding most likely refers to the "Piece of Cake" achievement/trophy, which is earned by completing a specific objective during the campaign . "Piece of Cake" Achievement Guide
: Save all your flashbangs and frag grenades specifically for this room. call-of-duty-ghosts
: Do not enter the room immediately. Stay behind the doorway for cover. The phrase "provide an piece" regarding most likely
To unlock this achievement (Gold Trophy / 100 Gamer Score), you must clear the common room in on Veteran difficulty without taking any damage. Stay behind the doorway for cover
: Throw everything you have into the room to clear out as many enemies as possible before they can react.
: Earned in Mission 6: "Legends Never Die" by killing 6 enemies with a knife while underwater. Call of Duty Ghosts: Piece of Cake Trophy/Achievement - HTG