It is a systemd service with a timer running approximately once a week. If you don’t use your computer for months, the service will run as one of the first things when you use your machine again.
You can see info about the service with commands
systemctl status archlinux-keyring-wkd-sync.service
systemctl status archlinux-keyring-wkd-sync.timer
and even look at the implementation files of the service:
/usr/lib/systemd/system/archlinux-keyring-wkd-sync.timer
/usr/lib/systemd/system/archlinux-keyring-wkd-sync.service
See also:
man systemctl
man systemd