What is the difference between foreground priority class and foreground thread boosting?
Foreground priority class boosts the priority class of the entire process (aka application, or program) that is in the foreground (meaning it has the focus of the keyboard and/or mouse). In contrast, foreground thread boosting only boosts the single thread in that in the foreground. A layman could consider a thread as a piece of a program, instead of the entire program. Its brother and sister threads in the same process are not boosted.