host
A host is the site a route runs on: the part of a web address that carries the registered name. One host can carry many routes, so a count of hosts and a count of routes describe the same services at two sizes.
The URI standard defines the host as a part of an address's authority, identified by a registered name or a numeric address. The path and any query that follow it identify a resource within that host. probe402 counts by the whole host name, so two subdomains of one domain are two hosts.
A host is not a seller. One operator can run many hosts, and one host can carry routes under many names, which is the arrangement the entry on a gateway describes. A count of hosts counts sites, and does not by itself say how many separate businesses stand behind them.
A route is one priced address on a host, and an endpoint is a route together with the request sent to it.
→ probe402 counted the hosts that quoted a price, and how much of a catalogue's listing count sat on a single host, in this issue of the Machine Commerce Reality Index.