From Halopedia, the Halo wiki
The Weapon Holder is a device used by the Covenant for storing certain weapons, using either anti-gravity or magnetic suspension to hold its cargo aloft. It is most often encountered in multiplayer levels holding the Energy Sword aloft, but can hold other weapons. It costs $3 and is available on every map.
Weapon Holders don't only hold weapons; they can also hold the 7 Wood (technically scenery) or any equipment like the Bubble Shield or Power Drain, and even some scenery such as the Gravity Lift, but it will only hold it sideways. Weapon holders can also hold the Active Camo, Overshield and Custom Powerups.
List of appearances