Classes!
One of the most important aspects of every being in this world. It quite literally shaped the path that any person would take as they progressed through life.
Classes determined a person's occupation, and it was universally accepted by every race as the only way to determine an individual's specialty.
Since certain Skills were exclusive to particular Classes, and the Class one chose determined their growth, type of training, and even means of living, selecting one was a very important decision to make.
There existed nine varieties of Classes, and under them were Specializations.
Usually, you would need to be very high-leveled to receive a Specialization. Thus, humans only had access to the nine primary Classes.
The requirements for getting a Class also depended on the race. For humans, reaching Level 15 ought to open the Class path for those who wanted to increase their abilities and obtain new Skills.
That said, not many humans reached this level.