This is the cast type skill for healing spells.

The in game help reads:

Skill duration: random.
Type of skill : spell casting skill (arcane skill).
Affecting stats: None.
It uses no endurance points.
One of the more benevolant types of magic, is the
magic which is used to heal one's self or others.
Not many things, once killed, are of any use to
anyone, so keeping things alive was one of the first
forms of magic that was utilized. Originally starting
as witch-doctors in various tribes, the art of healing
through magic has evolved to a very refined art. No
town within the realms is without a local healer.
It is a very dangerous world, so the art of healing
has been practiced and refined through the ages.
In order to use healing magic effectively, some
knowledge of the nature of this type of magic is
required.