The following is a description of the different states.
The term enabled and disabled was originally used when HealBot had different spells for each state. In modern HealBot this is no longer the case with the only difference being opacity.

A bar is enabled if

• In combat and Health is below the Alert Level - In Combat setting on the Skins Frames Bars Visibility tab or tanking
• Out of Combat and Health is below the Alert Level - Out of Combat setting on the Skins Frames Bars Visibility tab
• Out of Combat and a buff is required
• A debuff exists

A bar is disabled if

• In combat and Health is above the Alert Level - In Combat setting on the Skins Frames Bars Visibility tab and not tanking
• Out of Combat and Health is above the Alert Level - Out of Combat setting on the Skins Frames Bars Visibility tab
• No buff is required
• No debuffs exist