What are OG Jordans?

Hey there, could you tell me a bit about OG Jordans? I've heard they're pretty sought after in the sneaker world, but I'm not entirely sure what sets them apart from other Jordan sneakers. Are they a specific model or just a term used to describe vintage Jordans? And if so, what makes them so valuable and collectible? I'd love to learn more about their history and why they're such a big deal in the sneakerhead community.