Which type of network spans a single building or campus and provides services?

Small,closed Networks are usually some kind of (W)LAN ((Wireless) Local Area Network) which use Routers and Ethernet-Switches to provide the communication channels for network based software, since the LAN itself is just the infrastructure.

Larger networks may be split into logical units using VLAN (Virtual Local Area Network).

Clients outside the LAN can for example use Browsers (web) or VPN to connect to the machines inside the network.