What is "telluric current"

n. An extremely low frequency electrical current that occurs naturally over large underground areas at or near the surface of the Earth.

A telluric current (from Latin tellūs, "earth"), or Earth current, is an electric current which moves underground or through the sea. Telluric currents result from both natural causes and human activity, and the discrete currents interact in a complex pattern. The currents are extremely low frequency and travel over large areas at or near the surface of the Earth.