Plan position indicator
From Glossary of Meteorology
plan position indicator
(Abbreviated PPI.) A type of radar display on which the reflectivity or other properties of echoes are plotted in plan position, forming a maplike display, with radial distance from the center representing range and the angle of the radius vector representing azimuth angle.
The PPI is usually produced by scanning the antenna in azimuth with the elevation fixed. It may be an intensity-modulated display or may use a scale of colors to represent the values of the function displayed.