Slipstream space (Earth-2915)

Slipstream space, colloquially known as slipspace, or the Slipstream and formally known as Shaw-Fujikawa space or subspace by the United Nations Space Command and the Union of Progressive Peoples, is a dimensional subdomain of alternate spacetime consisting of eleven non-visible infinitesimal dimensions used for faster-than-light travel. Making a transition from one place to another via slipspace is known as a "slip", or "jump". A device which allows a spacecraft to perform slipspace transitions is generally referred to as a slipspace drive.

Source

 * https://www.halopedia.org/Slipstream_space.