A photonic shockwave was a release of energy which could be created by detonating a photon or photonic torpedo with a directed energy weapon. Extremely powerful, such a shock wave could 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 shockwave 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")