Bonus healing is extra healing added to spells. This is a primary way that healers increase both their efficiency as well as their raw healing power. This is typically seen on items as "increases healing done by spells and effects by up to X" or "+X Healing Spells". Additionally, since Patch 2.3, items with bonus healing were given bonus damage roughly equal to 1/3 of the amount of healing. This is typically referred to as "plus healing".
The actual increase that bonus healing will add is determined by the spell coefficient.
The following random suffixes include bonus healing:
|...of Healing||+ Healing|
|..of the Hierophant||+ Healing|
|..of the Physician||+ Healing|
|..of the Prophet||+ Healing|