A vector trap is a mechanism found in Orbital Frames that compresses space in a certain radius around the Orbital Frame. The range of the Vector Trap itself varies with Orbital Frames.
The orbital frames Anubis and Hathor are able to use their vector traps for an effect described as the same as a Urenbeck Catapult to essentially teleport themselves while Jehuty and Dolores make use of this mechanism to store weapons and other items.
A Vector Trap creates a sort of "hammerspace" and is used to explain how Jehuty is able to carry its sub-weapons. In the anime, Dolores makes use of it to store various mines as well as its own version of Jehuty's familiar weapons, such as the Halberd.
It should be noted, the concept of using negative mass and other exotic particles, like negative matter, to create folded regions of spacetime exists in physics. And the idea of using it as a pocket region of space, or "hammerspace", while extremely advanced is plausible using negative mass or exotic particles with negative mass. It's likely then that Metatron may be a form of negative matter. This would also explain Zero Shift technology, since the region of folded space would allow faster-than-light travel.