There are rules governing how data is transferred over networks, how they are compressed, how they are presented on the screen and so on. These set of rules are called protocols. There are many protocols, each one governing the way a certain technology works. For example, the IP protocol defines a set of rules governing the way computers use IP packets to send data over the Internet or any other IP-based network. It also defines addressing in IP. Likewise, we have other protocols like:
TCP: Transmission Control Protocol, used for the reliable transmission of data over a network.
HTTP: Hypertext Transfer Protocol, used for transmitting and displaying information in the form of web pages on browsers.
FTP: File Transfer Protocol, used for file transfer (uploading and downloading) over the Internet
SMTP: Simple Mail Transfer Protocol, used for email
Ethernet: Used for data transmission over a LAN.
Wi-Fi: One of the wireless protocols.
There are hundreds of other protocols ruling transmission of data over networks.