First bullet Second bullet What does it mean?

There are two ways to say it:

1, Japanese usage, such as the first 弾, that is, だい い ち だ ん

By the Chinese language is the first time, the first episode, the first paragraph and so on.

2, the bullet, that is, the barrage (barrage), the Chinese popular words, the original meaning of a large number or a small number of artillery to provide intensive shelling. The barrage, as the name implies, is a curtain formed by a lot of bullets, and the effect of a large number of trolling comments floating across the screen looks like the barrage in a flying shooting game.

Expanded:

Pop-ups give viewers the impression that they are interacting in real time.

The traditional player commenting system is independent of the player, so the content of the comments is mostly centered on the entire video, which is not very topical, and does not have the feeling of "real-time interaction".

Reference:

Baidu Encyclopedia -Pop-ups