In dbhost — Configuration Parameters — Nextcloud latest Administration Manual latest documentation:
Your host server name, for example localhost, hostname, hostname.example.com, or the IP address.
The description is a bit unclear about what a "host server name" is. I would suggest expanding it into:
The host server name/address for Nextcloud to connect to the database service, for example, localhost, hostname, hostname.example.com, or the IP address.