- Not available on that edition (the reason is in the tooltip)
- Depends on the setting, your class or another addon (details in the tooltip)
What it does
Checks the Balance Druid Eclipse bar: whether it is heading toward a Solar or a Lunar Eclipse, or how its energy compares with the number you set.
Why you might use it
Choose the measure first. Direction matches while the bar is heading toward the Eclipse you pick, so you can save Starfire for the Solar side and Wrath for the Lunar side. Energy compares the bar itself, from -100 (a full Lunar Eclipse) to 100 (a full Solar Eclipse), with the operator and value; only the fields of the chosen measure are used. Wrath of the Lich King through Mists of Pandaria only, and only for a Druid.
Example
your Eclipse bar is heading toward a Solar Eclipse
Settings
What each setting in the condition editor means, from the game's own help.
Balance Druid Eclipse. Choose the measure first. Direction matches while the Eclipse bar is heading toward a Solar or a Lunar Eclipse. Energy compares the bar itself, from -100 (a full Lunar Eclipse) to 100 (a full Solar Eclipse), using the operator and value. Only the fields of the chosen measure are used.
Operator - How to compare Eclipse with the Energy value. This comparison uses basic mathematical comparison operations.
Energy - The Eclipse bar, from -100 (a full Lunar Eclipse) to 100 (a full Solar Eclipse).