The Advanced Transit Association (ATRA) has provided this definition of Personal Rapid Transit (PRT):
Group Rapid Transit (GRT) has a similar definition but uses larger vehicles (typically up to about 25 passengers) and often incorporates intermediate stops. Modern PRT deployments often encourage ridesharing and the lines between PRT and GRT are becoming blurred. The term Automated Transit Networks (ATN) is a useful umbrella term incorporating both PRT and GRT. It is used interchangeably with PRT in this website.
The key technology distinction between ATN and other guideway systems is that the switching is in the vehicle. The rails (guideway) do not move. This is what enables very short headways (times between vehicles) and offline stations