The glossary below contains many of the terms you will find in common use throughout our website. Please refer to this list to find definitions of terms and answers to other Internet security-related questions.


A set of rules for encoding and decoding data so that messages can be exchanged between computers and so that each computer can fully understand the meaning of the messages. On the Internet, the exchange of information between different computers is made possible by the suite of protocols known as TCP/IP. Protocols can be stacked, meaning that one transmission can use two or more protocols. For example, an FTP session uses the FTP protocol to transfer files, the TCP protocol to manage connections, and the IP protocol to deliver data.

A method or predefined set of rules by which two dissimilar systems can communicate.