Perhaps the most interesting notion from the string and brane construction of reality is the large number of spatial dimensions required to support it, although most have an expanse so small that we cannot perceive them, much as an ant on a string can only perceive one axis of motion available to it. However, under certain conditions, a mathematical expression, the Yau-Calabi expression, can translate between the potential arrangements of these dimensions. Shaped correctly, a potent energy field according to this mathematical relationship can , for a short distance, rearrange these same dimensions into one more convenient forms for travel.
Effectively, this engine translates six of folded spatial dimensions of normal space into six unfolded dimensions, while for the ship, the three spatial dimensions of normal space are folded to a vastly smaller space. Chosen by the formative mathematics, this reversal of the dimensions of space is not quite symmetric with real-space. The practical effect is that while the distance between real places is vastly reduced, it is not quite eliminated. Interstellar travel is a matter of hours to weeks, however, rather than the centuries and millenia of real space. The Yau-Calabi Fold cannot be maintained within deep gravitational wells, as the transformation is too computationally intensive - the rapid changes in spatial distortion lead to the collapse of the field... and possibly the collapse of the ship. Generally, the Foldship must be a significant distance from any star or planet, but generally not more than a few days travel away from the star.
For reasons of performance, the average star-fighter or pleasure craft is not equipped with a Yau-Calabi Fold Drive. They are simply too massive to justify their inclusion. Instead, the majority of militaries deploy carriers, which launch waves of fighter craft. Mercenary and freelance companies frequently work on the same basic principle, although their carriers are typically modified freighter ships, rather than dedicated warships. It is the rare freelancer indeed that has both the contacts and the cash to purchase even a cruiser, let alone a carrier.