GaN stands for gallium nitride and it is a semiconductor material that's replaced traditional silicon in modern chargers. GaN devices switch at much higher voltages and are quicker than silicon and generate less heat and providing more efficient electrical conversion. The payoff in real life is a charger that's significantly smaller than earlier 65W versions and that operates cooler and safer as well. The foldable plug design means you can simply toss it into your bag without the prongs scratching your laptop or sticking anything.
I'm amazed by how compact powerful chargers have become. You can now get a 65W charger that fits comfortably in the palm of your hand, something that wasn't possible a few years ago. This miniaturization is thanks mostly to the switch from silicon transistors to gallium nitride (GaN), which allows manufacturers to produce smaller units that are more robust. Adding more ports is the most obvious move, but lately we've seen a new trend built-in retractable cables.