"Tesseract technology" is the use of fourth-and-fifth-dimensional mechanics in a three-dimensional reality.
By manipulating time and space, once can create a bubble of reality in a place as small as a molecule but as vast as the mind can envision. Dimensionally-speaking, this is not a sub-atomic reality, as all of the three dimensions of this new reality remain intact. Rather, this reality exists in a pocket that is reduced by time and space into the size of a molecule.
Through tesseract technology, one could literally store a whole army of devices and weapons, accessible on command, or create hideouts that cannot be seen by normal methods or accessed outside of a specific dimensional passageway.
It was also referenced and explained in the video series "Ask Captain Catastrophe".