It's truth in advertising. It's literally earth ground.
Oh wait. No, it's charcoal. Oh, I get it. A "purifier". Ahhhh yeah.
Also note the gold-plated SMB (in the second photo anyway) connector. Very important for those 20 KHz signals. We don't want any distortion VSWR introduced by the connector before it encounters the open circuit 0.0000000001 wavelength later.