- 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 your main-hand weapon's attack speed in seconds compares with the number of seconds you set, or your off-hand weapon's when Off Hand is ticked, or your ranged weapon's when Ranged is ticked. With no off-hand weapon equipped, an off-hand check does not match.
Why you might use it
Compares your main-hand, off-hand or (with Ranged ticked) ranged weapon's current attack speed, in seconds between swings. Since haste changes it, it can tell you when a haste effect such as Flurry or Slice and Dice is up, or whether you are holding a slow two-hander suited to a Slam rotation. With no off-hand weapon, an off-hand check is false (and true under NOT). On Retail and WoW Forever the game can hide this value, and the condition is unavailable while it does. See also Weapon Swing Time Remaining and Weapon Type.
Example
Your main hand weapon attack speed is less than 2.5 seconds
Settings
What each setting in the condition editor means, from the game's own help.
Off Hand - Should this condition affect your main or off-hand weapon. If this is checked, it will affect your off-hand weapon, otherwise it will affect your main-hand (or two-handed) weapon.
With no off-hand weapon equipped, an off-hand check is false (and true under NOT).
Ranged - Measure your Auto Shot or wand shot instead of a melee weapon. Choose Off Hand or Ranged, not both. The time remaining needs the combat log, so it works on Classic Era, Burning Crusade and Mists of Pandaria but not on Retail or Forever.
Operator - How to compare Attack Speed with the Seconds value. This comparison uses basic mathematical comparison operations.
Seconds - The amount of time (in seconds) between swing times for your weapon.