- 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 how many enemies you have at least the threat level you choose on, compared with the number you set. Only enemies within nameplate range are counted.
Why you might use it
Counts the enemies on which you have at least a given threat situation, so a tank can decide when to use area threat: Thunder Clap, Consecration or Swipe when you are securely tanking fewer mobs than are around you. Damage dealers can use it to hold area attacks while they are pulling threat on several enemies. Only enemies within nameplate range count, set in the game's interface options. On Retail and WoW Forever the game can hide threat, and the condition is unavailable then. See also Threat.
Example
the number of enemies you are securely tanking is less than 3
Settings
What each setting in the condition editor means, from the game's own help.
Threat - The minimum amount of threat you have with other units.
no threat risk - You are not in danger of taking threat away from whoever has threat.
higher threat than tank - You are in danger of pulling threat away from the current tank, and should reduce the amount of threat generated (by using threat-reducing abilities or ceasing DPS or Healing) immediately.
tanking, at risk - You are currently tanking, however you are not at the top of the threat table, and thus are at risk of them switching targets to somebody else.
tanking, secure - You are currently tanking and are not at risk of them switching targets at the moment.
Operator - How to compare Threat Count with the Count value. This comparison uses basic mathematical comparison operations.
Count - The number of units you have at least Threat on.
Threat is measured only on units within a maximum measurable range. The maximum range is set using Game Options -> Interface -> Game tab -> Names -> Nameplate Distance.