DNS
Domain name server to convert names to IP address and vice-versa. Runs on UDP/53 (with TCP/53 fail over).
When encapsulating data for transmission, the Network Layer will add the IP source and destination address. However, the destination address need not be an IP address; rather, it can be a FQDM. Thus the need for DNS.
It is a distributed system balanced across many different servers; usually managed by ISP or enterprise IT department. Typically an enterprise will have internal DNS servers for resolving internal domains; whenever an internal DNS server doesn’t know a specific address, it can forward requests to public DNS servers using UDP/53.
DHCP
Dynamic host configuration protocol, runs on udp/67,68. Used to assign IP addresses.
Enterprise set ups will have redundant DHCP servers.
File server
Centralized storage of documents and stuff.
On Windows the protocol is usually SMB, while with iOS it is AFP (Apple Filing Protocol).
Print server
This can be a computer connected to a printer, or a printer with networking capabilities.
Standard protocols: SMB, IPP (Internet Printing Protocol), LPD (Line Printer Daemon).
Mail server
Usually managed by IT or ISP because they are complex. One of the services running 24/7.
Syslogs
This is a protocol used to a logging server, usually integrated into a Security Information and Event Manager SIEM.
Authentication
Alows authentication for resouces via centralized management. Almost always an enterprise service, not often used in SOHO.
Usually a set of redudant servers, since without this no-one would be able to login.
UTM
Web security gateway / Unified Threat Management
They do URL filtering, malware inspection, spam filters, Routers, switches, firewalls, etc.
SCADA / ICS
Supervisory Control and Data Acquisition System / Industrial Control System
This manages industrial machines