Immortality is the ability to possess a possibly infinite lifespan. Immortals are protected from natural death, but can be killed or vanquished by magical powers, spells and potions or through physical harm.
Immortals may possess an arrested aging process, meaning they will not visibly age. When a being is born immortal, this generally means that they will stop aging once they reach maturity. Others simply age at a much slower rate than mortals.