Panchromatic stems from the greek Pan = "the whole" and chroma = "colors", literally the "whole colors" in one band. Which means that the sensor is unable to distinguish the different bands in the visible range.
PAN = panchromatic data means a single band that covers the entire visible and NIR spectrum from blue to NIR. It is black and white as it is a single band. Landsat offers PAN data at 15 m resolution.