Healing Mastery is a skill in the Heavenly Light skill tree of the Mage class.

Skill Description: Increase healing spell's ability for x%
Required job: Third Job
Required skill(s): Instant Advanced Healing and Superlative Healing
Required points: 55 points in Heavenly Light
Skill type: Passive Skill
LevelIncrease percentage
1 10%
2 20%
3 30%

The passive healing spell which increases the strength of your heals for free. Has a lot of requirements though, but if they're all met, then this should have 3 points in.