This is how many comments your video got.

Comments can be a good indicator of how engaged your audience is. Bots are big on YouTube though, so this can be misleading. Look at the actual comments before making a judgement on this stat.

Some creators find that asking people to comment has contributed to some of their videos going viral. It really isn't clear if this is true or not, but it's worth experimenting with. You should really read the comments, you'd be surprised how much you can learn.

As you get bigger, you'll get more comments. A lot of them will be spam/garbage/uninformative. Don't be afraid to use some other software tools to analyze the comments sentiment on bigger videos (filtering out spam). You can learn a surprising amount about your audience this way, depending on your channel.