- 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 seconds ago the combat event you choose happened to the unit specified, compared with the number of seconds you set. Events older than the Combat History Memory setting are forgotten.
Why you might use it
Compares how many seconds ago a unit's chosen combat event happened; the action is what happened to that unit, so 'your target was dodged' means your target dodged an attack. That fits reactive abilities with a short window, such as Overpower in Classic Era and TBC, usable for a few seconds after the target dodges. Only you, your pet and your target can be chosen in the editor, and events older than the Combat History Memory setting are forgotten. See Combat Action History to look back by position instead; on Retail and WoW Forever an event the game hides makes the condition unavailable.
Example
your target was dodged less than 5 seconds ago
Settings
What each setting in the condition editor means, from the game's own help.
Unit - The unit this condition uses as the target of comparison.
Action - The kind of combat action to look for (Hit, Miss, Parried, etc).
Operator - How to compare Combat Action History Time with the Seconds value. This comparison uses basic mathematical comparison operations.
Seconds - How far back in Unit's combat history to look for Action (by time). The condition matches when any recorded combat action of that kind happened a number of seconds ago that passes the comparison; for example 'is less than 3' means it happened within the last 3 seconds. Each combat action is treated separately. Combat actions older than Combat History Memory (seconds) (set in the primary Rotation Master configuration screen) are not available.