A covariant pulse was a burst of energy that could be transmitted over interstellar distances.
In 2373, after his salvage team was trapped aboard Empok Nor by soldiers of the Cardassian Third Order, Miles O'Brien devised a plan to contact Deep Space 9 by modifying the field coils of the station's deflector array to emit covariant pulses, communicating in a way analogous to a telegraph. However, they were only able to enact the plan after they managed to neutralize Elim Garak, who had become murderously hostile following exposure to a psychotropic drug that amplified his people's xenophobic tendencies. (DS9: "Empok Nor")