A schematic of the Enterprise-D's course through a rupture
In physics and mathematics, spacetime, or more fully as the spacetime continuum, is the singular continuum in which three-dimensional space and the singular dimension of time co-exist.
When a starship reaches the speed of warp 10, it goes into subspace and exists at every point in space at once, in superposition. (VOY: "Threshold") Exceeding warp 10 would allow a starship to travel backwards in time. (TNG: "Time Squared")
According to Spock, "In order to function, the galactic creation point must extend through space, time, into another dimension where the logic of things is totally different." (TAS: "The Magicks of Megas-Tu")
The Krenim weapon ship, used by Annorax, worked by pushing the target outside the spacetime continuum, thus deleting it from history. (VOY: "Year of Hell")
Disruption to the spacetime continuum can have serious repercussions. In 2368, for example, the USS Enterprise-D unknowingly entered a rupture in the spacetime continuum, which threw the ship and its crew into a temporal causality loop, experiencing the same time frame over and over. (TNG: "Cause And Effect")