What is "o=. main" in the output of the apt-cache policy command?

In the output of apt-cache policy command I see the following lines:

500 https://repos.insights.digitalocean.com/apt/do-agent main/main amd64 Packages
     release o=. main,a=main,n=main,l=. main,c=main,b=amd64
     origin repos.insights.digitalocean.com

What o=. main mean?

I also want to understand what this means for automatic updates. I see that the do-agent package is periodically updated with unattended-upgrades.

Although in /etc/apt/apt.conf.d/50unattended-upgrades I see only this:

Unattended-Upgrade::Allowed-Origins {
    "${distro_id}:${distro_codename}";
    "${distro_id}:${distro_codename}-security";
    // Extended Security Maintenance; doesn't necessarily exist for
    // every release and this system may not have it installed, but if
    // available, the policy for updates is such that unattended-upgrades
    // should also install from here by default.
    "${distro_id}ESMApps:${distro_codename}-apps-security";
    "${distro_id}ESM:${distro_codename}-infra-security";
//  "${distro_id}:${distro_codename}-updates";
//  "${distro_id}:${distro_codename}-proposed";
//  "${distro_id}:${distro_codename}-backports";
};

I think it means origin=, the term behind you can put in the unattended updates like this: o=Docker -> "Docker:${distro_codename}"; in /etc/apt/apt.conf.d/50unattended-upgrades.

But for some reason it doesn't work with Icinga: "ubuntu icinga-jammy:${distro_codename}";