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 unit of data that is formed when a protocol breaks down messages that are sent along the Internet or other networks. Messages are broken down into standard-sized packets to avoid overloading lines of transmission with large chunks of data. Each of these packets is separately numbered and includes the Internet address of the destination. Upon arrival at the recipient computer, the protocol recombines the packets into the original message.