"ISO" stands for "In Search Of" on Facebook, and it's commonly used when someone is looking for a specific item, service, or information. For example, if a user posts "ISO: recommendations for a good local restaurant," it means they are seeking suggestions or recommendations for a restaurant in their area. The acronym "ISO" is often followed by a description of what the user is searching for, and it can be used in various contexts, including buying and selling items, seeking advice, or finding resources.