two-factor authentication - Definition from the Hotspot Shield Glossary
As the name implies, two-factor authentication requires an additional level of authentication from a user on top of the conventional username and password. In standard authentication, a user is required to enter a username or email and a password - While these items should be unique to the user, there is the potential to illicitly obtain this information to hack the account.
Adding a second layer of authentication decreases the chance of a user’s account being hacked and personal information stolen. The second factor of authentication could be a security question that only the user will know the answer too such as “What was the name of your first pet”, a further piece of personal information like a telephone number or date of birth, or even a CAPTCHA (A code that has to be entered that matches a computer generated image). The techniques involved in two-factor authentication are continually evolving and become more secure.