Tails is a live system that aims to preserve your privacy and anonymity. It helps you to use the Internet anonymously and circumvent censorship almost anywhere you go and on any computer but leaving no trace unless you ask it to explicitly.
It is a complete operating system designed to be used from a DVD, USB stick, or SD card independently of the computer’s original operating system. It is Free Software and based on Debian GNU/Linux.
Tails comes with several built-in applications pre-configured with security in mind: web browser, instant messaging client, email client, office suite, image and sound editor, etc.
Tails relies on the Tor anonymity network to protect your privacy online:
all software is configured to connect to the Internet through Tor
if an application tries to connect to the Internet directly, the connection is automatically blocked for security.
Tor is an open and distributed network that helps defend against traffic analysis, a form of network surveillance that threatens personal freedom and privacy, confidential business activities and relationships, and state security.
Tor protects you by bouncing your communications around a network of relays run by volunteers all around the world: it prevents somebody watching your Internet connection from learning what sites you visit, and it prevents the sites you visit from learning your physical location.
Using Tor you can:
be anonymous online by hiding your location,
connect to services that would be censored otherwise;
resist attacks that block the usage of Tor using circumvention tools such as bridges.