A mass teleporter is a large portal capable of carrying large numbers of people in a short amount of time without a serious amount of stress or supporting magi.
Although many portals share characteristics with mass teleporters, only one true mass teleporter is known to have been created, and it was destroyed before it was perfected. Thus the phrase mass teleporter generally refers to this portal, which the Empire built at their Portal Fortress during the Empire-Avernum War. The teleporter was built on top of the old teleportation augmenter near the Northern Waters, which was incorporated in its design.
The teleporter was one of the lynchpins of Garzahd's war strategy; it was to be used to transport substantial elements of the Imperial Army into Exile. The destruction of the portal, by the Empire War Heroes, turned the project into a major loss for the Empire and was a major factor in their withdrawal from Exile.
One notable characteristic of powerful teleporters is their ability to damage space itself; this was demonstrated in the destruction of the mass teleporter, which created a rapidly spreading tear in space. The adventurers who destroyed the portal used the onyx scepter to repair the rift; it is estimated that, had it not been promptly contained, the portal rift would not have resolved itself without the obliteration of a substantial portion of Ermarian.