Maximum Power Point Tracking (MPPT)
The control algorithm an inverter uses to continuously adjust the voltage it draws from a PV array so the array delivers the most power available under the current light and temperature. The point moves constantly, so the tracker searches for it many times a second.
A solar module's current-voltage curve has exactly one point where the product of voltage and current is greatest, and that point shifts with irradiance, cell temperature and shading. Without tracking, an array connected directly to a fixed load would spend most of the day well away from it. All modern grid-tied inverters do this; where they differ is in how fast they re-acquire the point on a broken-cloud day and how well they cope with a shaded string, whose curve can have several local maxima and fool a naive tracker into settling on the wrong one.