From Zelda Legends Wiki
Spirits of concentrated hatred that fly around open fields and graveyards. Often they are blue- or white colored, and they wear a robe and a lamp.
These are the Ghosts of the Zelda series.
Poes in different games
A Link to the Past
The Poes in this game are mostly floating around, and when they hit Link, hit will only cause damage, nothing more. And when Link defeats a Poe, nothing happens. They are just normal ghost-like enemies floating in graveyards.
Ocarina of Time
The Poes of Ocarina of Time are making some float-noise when they move around, and they attack by swinging the lamp they have. When Link defeats a Poe, the Poe Spirit will stay in the "place of defeat" for a while, and Link is able to pick it up into a bottle. The Poe souls are sold in a shop, too.
The Poes of Twilight Princess are invisible to a normal human, but the wolf is able to see it by using the wolf sense. The Poes wear a scythe, and they wear a tall robe, and it's able to hit them only by jumping, because we all know, that the Poe's are able to float in the air. When Link defeat's a Poe, he will get a Poe's Soul. Those are used to free Jovani.
--Gameboy 12:42, 23 July 2007 (EDT)