Where does host.name come from?

Hi! I have fileabeat and logstash to send Nginx data to elasticsearch. I do not have “host.name” field in my logs, but when I discover my index patterns, I see this field. Where does it come from? How does elasticsearch understand the hostname?
Can someone explain this to me?

It's likely coming from Filebeat.

Could you please explain how it is configured automatically? Can I override it?