Authentication - Definition from the Hotspot Shield Glossary
Authentication is the process of identifying whether a person or device is who or what they say they are. In computing there is a great need for authentication to ensure the integrity and authenticity of data being transferred over networks and the internet. Without authentication, there would be no guarantee that persons or devices who are sending or receiving information are the correct intended party.
There are many forms of authentication, mainly user and machine. User authentication is where the user identifies themselves using a username and password for example, whereas machine authentication will occur automatically and use such things as digital certificates and keys. It is important to note that Authentication is different from Authorization.
Authorization determines whether the person or device is allowed to request authentication in the first place.