A warp pulse was a method whereby a starship could attain faster-than-light velocities by field-saturating the nacelles, firing the engines at maximum intensity and then disengaging them, allowing the ship to "coast" at warp speeds without actively employing the warp engines.
Such a method was utilized by the USS Enterprise-D in 2370, when it became necessary to rescue a Federation medical transport which had become stranded inside a subspace rift. As active use of warp drive within the rift would cause it to expand even further, Commander Data proposed the idea of using a warp pulse to enter the rift and beam the crew of the transport to safety. The plan worked, although the rift expanded while the Enterprise was inside due to the crew of the transport attempting to use their warp engines, temporarily stranding the Enterprise inside the rift. (TNG: "Force of Nature")