What does [::] mean in my nginx config file

I was looking at my nginx config file I noticed two this.

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    index index.html;
}

I understand this part listen 80 default_server; it tells nginx to listen on port 80 and set that as the "default_server" but I do not understand the second line.

listen [::]:80 default_server;

It appears I am setting the default server again on port 80 but I do not really understand the [::] part of it at all.

Can someone explain to me what this configuration does?

It is for the IPv6 configs

from the nginx docs

IPv6 addresses (0.7.36) are specified in square brackets:

listen [::]:8000;
listen [::1];