So what’s the app all about? Well, if you’ve used Facebook’s normal mobile app then you’ll no doubt have experienced the frustrations of accessing messages through the full app, so the Facebook Messenger app is for those who just want the ability to message their Facebook friends easily. Much in the same way as BlackBerry Messenger (BBM) works.
The app lets users send messages instantly to other friends, chat in real-time and create group conversations. Additionally, Facebook Messenger lets users attach photos and location information to messages.
Thanks to @AppsFire for the tip.