Warp highways, also known as space lanes, were regions of space where mass/energy differentials, subspace topography and geodesics, and other factors allowed for greater effective velocities when using warp drives or other similar means of faster-than-light propulsion technologies.
Early interstellar spacecraft would sometimes stumble onto one of these highways without noticing. If lucky, they might arrive at their destination sooner than expected; if not, they might find themselves significantly off course by the time they detected the problem.
Over time, starship navigators came to know these "shortcuts" and used them regularly when plotting a course, as the variable factors involved meant that the quickest route between two points in space was not always a straight line.
By the 24th century, the starfaring species of the known Alpha and Beta Quadrants were aware of the majority of such "lanes" in their local space. The Rigel, Canopus, Cygnus and Antares Highways were among the commonly used long-distance routes between the regional "cores" of explored space and the vast reaches beyond. (Star Trek: Star Charts; TNG novel: The Buried Age)