Messenger Communication app
Messenger is Facebook's messaging app and platform which lets you video call, chat and send photos and other content to your friends on the most popular social network. You can participate in conversations which are available later on any connected device.
Sharing of images, location, stickers and many more actions can be performed in Facebook Messenger, which can be used for personalization of conversations. The app has also support other third party services with the options to send short movies or GIF.
Messenger is great app which you can use to connect with any of your contacts even while travelling abroad. Avoid roaming charges and call friends even with a video call at no cost. Since messaging isn't available in Facebook app, Messenger is the main app to talk to your friends.
For a kid friend messenger refer to Facebook Messenger Kids.
Some of the latest updates about Messenger are the message threads. There is a good article about it on VentureBeat which covers it. You can also check out this collection of 24 tricks for Messenger from PCMag.