1. n. 
The convention adopted by the Society of Exploration Geophysicists (SEG) for the display of zero-phase seismic data. If the signal arises from a reflection that indicates an increase in acoustic impedance, the polarity is, by convention, positive and is displayed as a peak. If the signal arises from a reflection that indicates a decrease in acoustic impedance, the polarity is negative and is displayed as a trough. There is another standard for minimum-phase data. In order to interpret seismic data acquired at different times within a region, to model data, or to assess bright or dim spots, some knowledge of the polarity of the data is essential to correlate or tie data properly.