End-to-end encryption (E2EE) is a system of communication where only the communicating parties can read the messages. When implemented properly, E2EE prevents potential eavesdroppers – including telecom providers, Internet providers, and even the provider of the communication service – from being able to access and decrypt the messages exchanged or the cryptographic keys needed to decrypt the messages.
End-to-end encryption is intended to prevent data being read or secretly modified, other than by the true sender and recipient(s). The messages are encrypted by the sender and any third party that may have access to the messages can access them only in their encrypted form. Only the recipient can decrypt the encrypted message.
In places where encryption is implemented, but not end-to-end – i.e. email – messages between parties are typically encrypted while ‘in-transit’ but ultimately pass through trusted intermediaries that can access the plaintext messages.