A photonic shock wave is a release of energy which can be created by detonating a photon torpedo with a directed energy weapon. Extremely powerful, such a shock wave can be used to disable a small group of ships.
This tactic was used in the Battle of Vorkado, wherein a Romulan captain disabled two attacking vessels by creating a photonic shock wave between the ships. This battle was contained in The Doctor's tactical database after his upgrade to the Emergency Command Hologram. In 2377, he utilized the same procedure to disable two Quarren patrol ships which were attacking the USS Voyager. (VOY: "Workforce, Part II")