A space warp is a temporary space phenomenon caused by rare large concentrations of antigraviton particles which are able to distort space, much like normal gravity. Artificially, this is created also by a sufficiently large matter/antimatter reaction, taking place in space far removed from any strong gravity fields; otherwise, gravitic distortion will prevent the warp ever closing at all, exposing the ship to the force of the reaction.
The Morvan Drive sets a powerful, but tightly focused matter-antimatter reaction, generating enough antigravitons to create a localized space-time warp which is sealed by subspace. If a ship is correctly positioned at the very edge of the reaction's event horizon, it can hop across space instantaneously (usually 20% to 35% of a light-year away).
The gravitic mines use the principles of a space warp offensively, in order to engulf a target in the "well" and annihilate it to the subatomic level.