Since: 2008 (in China)
Meaning: Bullet curtain, countless live comments and reactions on videos.
The first time 弹幕 (dànmù) appeared in China was in 2008, but years before Japan had already experienced it through the N站 (Niconico). It consists in adding live comments and reactions on videos in a way that the video itself isn’t visible anymore. The video appears fully covered with words and symbols which run from one side to another.
So, when you watch a video covered by a bullet curtain running in front of you, just call it 弹幕.
Need to know: The most famous website in China where you can find thousands of videos covered with 弹幕 is bilibili.tv
Related words: 网红
In Use: “你看视频喜欢开弹幕吗？” (Do you like to turn on live comments and reactions while watching a video?)
“你就关弹幕吧！” (Just turn off live reactions and comments!)
Interesting things: Here a list of websites where you can find any kind of videos packed with comments and reactions! (And Keep calm, remember that you can always decide to turn them off!)