The headset on your scooter is the bearings and parts located on each side of the headtube. It is the headset that makes the fork spin around, so you have the opportunity to spin the bar when you perform tricks.
There are two types of headsets for scooters. The non-integrated is located on the outside of the headtube and is usually used on cheaper and more standard scooters. An integrated headset is standard for high quality scooters. It means that the headset is integrated inside the headtube, which gives a better spin and longer sustainability. When choosing a headset, you must make sure it has the same type of integration as the headtube on your stunt scooter.