Most (if not all) HPDE events, separate the participants into run groups based on experience level. The nomenclature of the groups varies widely. Some groups use numbers (HPDE1,2,3 etc), other use color codes (Green, Blue, White, Black, etc). No matter what they are called, the generally follow the same grouping:
Comprised usually of first-timers, or drivers with less than 2 or 3 events, this is where everyone starts. Your weekend will be spent getting used to driving on track. Some pick it up faster than others, so there is typically a wide range of speed differentials. You learn to deal with traffic pretty quickly here. Main focus is on smoothness and situational awareness.
Passing is almost always restricted to only the longest straights.
These driver's have shown their instructors and event stewards that they can be trusted on track, that they manage traffic and crisis well enough to start working on some more advanced techniques. Work on improving speed starts here. Many drivers will stay in the intermediate ranks until they get three or four events at each track close to them. Instructors are usually still mandatory for the intermediate group.
Passing may be opened up slightly compared to the beginner group, but is typically very limited.
Speed, consistency, technique, and car prep have advanced with the driver, and the advanced group is where ones craft is honed to perfection (at least as perfect as you want it to be.) Instruction in the advanced groups is typically offered, but is optional (depending on the organization.) Advanced techniques are perfected, limits are pushed and extended in this group. Track speeds are significantly higher than the beginner and intermediate group, as is the risks involved. Crisis management must be second nature.
Passing rules become more liberal. Most involve any straight, some groups allow passing in the turns in the advanced groups as well.
Usually reserved for highly prepped cars, or highly advanced drivers who are not instructing. Usually the fastest group at any event. Many racer drivers will utilize this group at an event before an upcoming race to shakedown a race car or get some relatively inexpensive testing time.
Passing is usually very liberal in this group.
The instructors need a place to drive as well... a hodegpodge of cars and speeds, very entertaining to watch.
Passing is usually very liberal, if not unlimited.