[microtonal]

The article literally states:

End to end encryption is a way of transmitting a message so that it can only be read by the intended recipient, and not intercepted by accessing the servers or the networks via which the message is sent.

Rather than being sent as plain text, the message is scrambled as a long series of digits that needs a key only held by the sender and the recipient to understand it.

The keys are ephemeral, meaning they disappear after the message is unscrambled so that it can not be unlocked afterwards.