An interphasic pulse was a high-frequency energy emission which was used to eliminate a series of organisms which had infested the USS Enterprise in 2370.
Lieutenant Commander Data's positronic subprocessor had detected the interphasic signature of the organisms, revealing their existence to the crew. Chief engineer Geordi La Forge was then able to modify Data's subprocessor to emit the interphasic pulse to eradicate the infestation. (TNG: "Phantasms")