Guild Wars 2

Are ghosts considered “undead”?

In achievements, there’s one for Risen and one for Ghosts. But the potion doesn’t say either, so I’m assuming it is named Undead to cover both.

Would it be good for AC?

Undead potions won’t work on ghost, I think. There’s a Sigil of Ghost Slaying and other for Undead Slaying. Also, there’s a potion for ghost slaying but you have to buy the recipe with ascalonian tears.