End-to-end encryption is when a communication channel is encrypted at the sender's end and never decrypted until it reaches the recipient's device. It is used in many messaging platforms such as WhatsApp. In contrast many email systems encrypt communication between end-user devices and the mail server, but messages are stored as plain text at the server.
End-to-end encryption ensures a high level of privacy but also means that it can be used for criminal purposes without the possibility of a 'tap' to read content. For this reason, some countries have tried to require a backdoor for law enforcement, including a high profile stand-off between UK government and Apple.
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