From Halopedia, the Halo wiki
For the fields used to contain pressurized spaces from a vacuum, see energy barrier.
Shield doors are energy fields that can repel plasma, gunfire, vehicles and virtually any other object, with some types exclusively allowing living beings to pass through. They are similar in design to bubble shields with differences being the color and infinite usage time. Anti-vehicle barriers are a larger-scale application of shield door technology.
There are several in past Halo games and they appear in Halo 3 on the multiplayer maps Epitaph and Snowbound. In the secondary versions of the maps Snowbound and Epitaph, namely Boundless and Epilogue, the map shield doors are removed.
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. 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.
List of appearances