You could add that it is a faith based system.
The two main strains: devotional and mystical; each having a definite element of faith.
In the first, that the Buddha did exist and continues to exist. Sworn to continue in connection with this reality until all sentient beings escape; thus the Buddha can be prayed to, and may aid a devotee.
In the second, that enlightenment (whatever it is) is possible and that one may possibly achieve it.