From Halopedia, the Halo wiki
The Sword Spree is a spree medal awarded in Halo 3 and Halo: Reach multiplayer, campaign and Firefight. In Halo: 3 it is awarded for killing five opponents in a row with the Energy Sword without dying. In Halo: Reach the medal does not require kills to be consecutive, just that the player kill five enemies with the Energy Sword without dying.
It is represented by a four-pointed star with an Energy Sword on a blue background in the center.