A host can be considered as a basic grouping unit in Zabbix configuration. As you might remember, hosts are used to group items, which in turn are basic data-acquiring structures. Each host can have any number of items assigned, spanning all item types: Zabbix agents, simple checks, SNMP, IPMI, and so on. An item can't exist on its own, so hosts are mandatory.
Zabbix does not allow a host to be left alone, that is, not belong to any group. Let's look at what host groups we have currently defined—from the frontend, open Configuration | Host groups:
The first thing that catches the eye is that the Templates group seems to have a large number of templates already. These are provided as examples so that you can later quickly reference them for some hints on items. We'll ignore these for now. We can also see an empty Discovered hosts group and the Zabbix servers group, which contains a single example host. The interesting part is in the first half of the table—we can see both...