Shield Door
From Halopedia, the Halo wiki
Shield Doors are Covenant and Forerunner made "doors" that are able to allow people and machines through while repelling plasma and gunfire. They are similar in design to energy shields that the Jackals wear.
There are several in past Halo games and they appear in Halo 3 on the multiplayer map Snowbound.
Now they are also featured as forge items in the new Heroic Map Pack and they can be placed anywhere.
If one stands exactly in the shield door's energy field, doing a melee or shooting in any direction will be negated by the shield. However, the player is still vulnerable from attacks from either side. This also works with the Bubble Shield. Although the Bubble Shield is similar to the Shield wall, it is still different because the Shield Wall doesn't allow vehicles to pass. By "overloading" a map with shield doors (Using excessive trip mines to cause the map to lose control of the maps graphical and geometrical assets), the shield doors on a map will disappear!
