A protocol is a set of rules that allows two devices to communicate.

TCP/IP

The transmission control protocol (TCP) is used for error free data transmission between two routers.

The internet protocol (IP) is used to route packets across a WAN.

Together they make up the TCP/IP protocol stack, which is the foundation of communication over the internet.

Ethernet and Wi-Fi

The Ethernet and Wi-Fi are sets of related protocols.

The Ethernet is a set of protocols used for communication on LANs.

Wi-Fi (a trademark) is a set of protocols for wireless communication. Networks that make heavy use of Wi-Fi are called WLANs.

HTTP/HTTPS

The hypertext transfer protocol (HTTP) is a way for clients and servers to send and receive requests for HTML web pages. It is the fundamental protocol of the world wide web WWW).

The hypertext transfer protocol secure (HTTPS) is HTTP with an added layer of encryption and authentication. It is used when a website needs to deal with sensitive information e.g. passwords and bank account details.

FTP

The file transfer protocol (FTP) is used for sending files between computers, usually on a WAN.

Often used through FTP clients, but it can be run from the command line.

POP/IMAP/SMTP

Used on mail servers to deal with email. Mail servers act like a virtual post office for incoming and outgoing mail.

The simple mail transfer protocol (SMTP) is used transfer outgoing emails from a client to an email server or from one server to another server.

The post office protocol (POP) is used to retrieve email from a mail server. The email is removed from the mail server when it is transferred to a device.

The internet message access protocol (IMAP) is also used to retrieve email from a mail server. The email is kept on the mail server when it is transferred, allowing synchronisation across devices.