An unexplored region of space where the Enterprise became trapped in a repeating temporal causality loop.
The Typhon Expanse is a largely uncharted region of space that the Enterprise enters for survey work. A rupture in the space-time continuum there traps the ship in a temporal causality loop that repeats the same events again and again.
In Cause and Effect, each cycle ends with the Enterprise destroyed after a collision with the USS Bozeman, which emerges from the same distortion. Data eventually sends himself a subtle message across the loops that lets the crew avoid the collision, and they learn that the Bozeman had been caught for roughly ninety years.