https://www.theverge.com/2017/9/11/16291740/facebook-instant-videos-feature-in-testing

Facebook is testing a new feature that makes sure you’ll always have videos ready to watch — and you won’t have to waste your data plan downloading them.

The feature is called Instant Videos, and it appears to download various Facebook videos while you’re connected to Wi-Fi so that they’ll be able to start playing immediately on your phone when you’re inside the app. The feature was first spotted by The Next Web’s Matt Navarra and was later confirmed by TechCrunch.