- 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 your pet knows the pet spell you choose and it is off cooldown. A spell held only by the global cooldown still counts as available.
Why you might use it
Check that a pet ability is known and ready, so the rotation can prompt you to use abilities your pet does not cast on its own. Examples are a Felhunter's Spell Lock to interrupt a cast (pair it with Cast Interruptible), a Voidwalker's Sacrifice when you are in trouble, or a Water Elemental's Freeze. On Retail and Forever this uses cooldown flags the game never hides. See also Spell Available and Pet Spell Cooldown.
Example
Spell Lock is available
Settings
What each setting in the condition editor means, from the game's own help.
The icon next to the spell name will automatically update to display the spell that is currently selected. You can drag a new spell from your spell book or action bars into this icon slot to replace your selected spell.
Use this exact spell rank - Unticked (the default), any rank of the spell matches. Ticked, only the rank you chose matches. (only on Classic Era, TBC Anniversary, Forever)
Spell - This is a specific spell used in this condition. You may drag this spell from your spell book or action bars into the input field or spell icon to set this value. This input field has prediction enabled, so you do not have to type the full spell name, just select from the prediction frame when it appears.