Variable geometry turbochargers (VGT), also known as variable nozzle turbines (VNT) are a type of turbocharger designed to allow the effective aspect ratio (A:R) or size of the turbo to be varied as power demands change. Variable-geometry turbochargers have a minimal amount of turbo lag and are very efficient at higher engine speeds.
https://en.wikipedia.org/wiki/Variable-geometry_turbocharger