Poes are enemies that appear in several Zelda games. They have the appearance of ghostly figures carrying lanterns which they usually use to attack Link
 Ocarina of Time
In Ocarina of Time, Poes usually appear when you move gravestones in Kakariko graveyard. Even though Link can use Z-target on them, they will turn invisible (except for the lantern) and Link won't be able to hurt them until they turn visible again. Their souls can be captured in a bottle and sold to the Poe Salesman. There also another variations of Poes in Hyrule Field (when Link is an adult) that will try to throw fire at Link if he tries to chase them. These won't turn invisible when Z-targeted, but will disappear completely if they get too far from Link. Another type of poe is the Big Poe, which souls are required to obtain an empty bottle.
 Majora's Mask
Poes's behaviour in Majora's Mask is basically the same as the ones from Ocarina of time, but they are much rarer. They appear in one room in the Stone Tower Temple. There are also two Big Poes in the subterrean areas of Ikana Canyon. The Poe Sisters are also present in this game and are part of a mini-game.
Related Threads2 poe souls in cave under Hyrule field north of castle??? - last post @ May 30, 2012
Cant find last Poe! - last post @ Jun 8, 2014
Arbiter's Grounds Temple : 4 poes with blue fire before the gate... please help!! - last post by @ Jun 17, 2007
Can't find last poe. Is a bug possible? - last post by @ Jul 5, 2007
Big Poes... - last post by @ Sep 18, 2007