Big Poes are large ghosts that are hiding around Hyrule Field in The Legend of Zelda: Ocarina of Time remake. Like regular Poes, you can store Big Poes in bottles, and sell them to the Poe Collector in Hyrule Castle Town. However, Big Poes are worth a whopping 30 rupees, so if you collect them all, you'll get a good chunk of change.
Polygon.com
All Big Poe locations in Zelda Ocarina of Time
Shown as published in the source's RSS feed. IndiaAIFounders doesn't link out to third-party sites — this is the complete detail available from the feed itself.