Nearby Friends allows you to share your location with, well, nearby friends. You can elect to have your location open to share for a few hours, or indefinitely. It also will reveal the approximate distance between you and your pals. Users must opt-in to use the feature. By clicking on a "+" sign, you send a notification to a friend that asks him to opt-in
The update for the iOS version of Facebook is available now in the App Store.
Facebook app for iOS is updated to version 11.0
1. Nearby Friend shows you how far away your pals are from you
2. Send out messages to get your friends to activate the feature
source: Facebook via TechCrunch