A host is simply some device that connects to a network. Most commonly this refers to a workstation or a server.
Similar terms are endpoint and node; These also refer to something connected to the network.
However, these terms do not generally refer to network equipment like routers, switches, or access points.
Traditionally the term host was used, as computers were hosting resources that could be shared, like web pages, files, printers, and so on.
Host may also be used to describe a physical server that contains one or more virtual servers. But that’s another topic…