(1) (n). Geophysics. An electromagnetic method that uses electrodes with time-varying currents and voltages to map the variation of electricalpermittivity (dielectric constant) in the Earth at low frequencies. Induced polarization is observed when a steady current through two electrodes in the Earth is shut off: the voltage does not return to zero instantaneously, but rather decays slowly, indicating that charge has been stored in the rocks. This charge, which accumulates mainly at interfaces between clayminerals, is responsible for the IP effect. This effect can be measured in either the time domain by observing the rate of decay of voltage or in the frequency domain by measuring phase shifts between sinusoidal currents and voltages. It is often used inexploration for minerals and can sometimes distinguish different types of mineralization. The IP method can probe to subsurface depths of thousands of meters. Alt. form: induced polarization. (2) (n). Drilling Fluids. Abbreviation for the Institute of Petroleum, a standardization body for the petroleum industry in Europe. Several industry-standard drilling-fluid tests are adopted from IP and ASTM procedures. See: API, aromatic content test, ASTM, flash point, ISO