- 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 if the game reports a boss encounter in progress. It needs no boss mod.
Why you might use it
A light way to tell a boss fight from trash: spend your major cooldowns only while an encounter is running, or switch to a boss rotation. It starts when the encounter starts and ends on a kill, a wipe or a reset, and it knows nothing about which boss or which stage it is; use Boss Mod Encounter for that. It reads in combat on every edition, including Retail and WoW Forever.
Example
a boss encounter is in progress
Settings
What each setting in the condition editor means, from the game's own help.
Matches while the game says a boss encounter is in progress. Unlike the Boss Mod Encounter condition it needs no boss mod, and it knows nothing of which boss or stage it is. It starts when the encounter starts and ends on a kill, a wipe or a reset. It reads in combat on every edition, Retail and Forever included.